Good guide, but you are missing ALOT of points.
You've skipped on the PvP zones altogether, missed Spetznaz and Shivans, and there are some bits and pieces you've skipped on.
I'll help:
Overview Correction: Just something quick to revise: Each island's governor takes control of the Commercial operations on the island. The Marshall is the Military Governor of the Island, and is entrusted in keeping the peace of the area.
Zones you Forgot (Excluding Sirens Call since it's not a RI zone so to speak):
Bloody Bay: Used to be a vital checkpoint in the slave trade to the Americas. However, after a massive slaughter of a Slave rebellion (from which it got the name), it saw alot of inactivity after 1865. In the late 80's, however, a meteor shower struck the island exclusively. The meteor shower consisted of 6 meteors that slammed into the island in various locations. The meteors then proceeded to irradiate the island, and from it spawned the Shivans. Longbow has a major base of operations on the island, both to act as a "peacekeeping" force to evacuate the few citizens still marooned on the island and to spite Arachnos by getting an easy checkpoint to further operations in West Rogue Isles.
Warburg: Not alot is known about Warburg so far, but this is what I know.
Prior to the Arachnos coup in the 50's, the island was largely unused... Apart from a massive 5th Collumn base underneath the island. From what I can understand, the Island was probably used as a secret muster point for units planning to attack Independance Port. However, after WW2 ended, the 5th Collumn poured their resources to create a missile facility on the island. If their plan would have worked, it would have caused an early Cuban Missile Crisis. However, in the 50's, Arachnos struck at the island, overthrew the 5th, and captured the base. Many soldiers died to take Warburg, and the name itself is a memorial to those fallen to take it.
After that, the island was settled. Arachnos continued to manufacture rockets under the isle, and perfected the VENOM Rocket sometime between 2000 and 2005. But, due to the recent events transpiring in America, Lord Recluse has turned a blind eye to Warburg, mainly because, apart from a Commercial and Warehouse area, did not really have any problems.
However, the Military Governor of Warburg, Marshall Brass, decided that Lord Recluse was weak, and didn't want to use the VENOM rockets at all. Somehow, he rallied the Garrison of Warburg, comprised of the second best Island Garrison (The first being Grandville) of the Rogue Isles, and broke off from Arachnos.
To retalliate, Lord Recluse sent a very small and weak division of Wolf Spiders to keep the Rogue Elements from thinking that Recluse really doesn't care about them (Which would probably lead to other Governors breaking off). But really, Lord Recluse could easily wipe the Rogue Elements from the Island. But he has a greater plan for it apparently.
Groups you forgot:
Shivans: These globs of extraterrestrial matter originated from a meteor discovered in the 70's by an Indian scientist. The meteor was enormous, around the size of Maine, and worst off, it was heading straight for Earth. The scientist named it Shiva, after the Hindu God(dess? I'm not sure

) of Destruction. Relaying this info to the US Government, the US contacted the Freedom Phalanx to try to stop Shiva. (Note: The rest of this stuff I'm just making educated guesses on) The Phalanx sent Cassiopiea (A statue of her seen in Paragon City Hall) to destroy it. She succeeded, but not completely.
In the late 80's, Shiva finally came to earth... In the form of 6 small meteors that crashed on Bloody Bay. Most of the Islands population fled after the impact, many died from radiation poisoning brought by the meteors, and some lucky few survive to this day, but barely.
The Shivans themselves are globs of what appears to be radioactive goo. They can suck up biomatter (Be it trees, mold off rocks, or even the remains of humans) and use it to build somewhat crude forms. These forms, I can assume, seek out more biomatter to waste down and absorb.
Currently, the Shivans are being studied on Bloody Bay, although Dr. Aeon (Or possibly Prof. Echo) has recieved a number of them and is keeping them in a lab in Cap.
Spetznaz: They appear to be a meta-human merc group originating from the Soviet Union. They employ normal, altered, and meta-humans in their forces. Currently, their only prescence seems to be the reaquisition of one of their former scientists, Dr. Krylov.
Rogue Arachnos: Under the leadership of Marshall Brass, the former Elite Garrison of Warburg has broken off from Arachnos and is holding the VENOM rocket system, as well as the multitude of labs devoted to Arachnoid Research and Replication, hostage. They do employ Hercules Titans from Malta Group, in exchange for Arachnoids Data and the occasional nuke. Currently, it doesn't seem like Lord Recluse is all that interested in negotiations with Brass, but more or less to see his Destined Ones in action against Rogue Elements.
Corrections to Islands and Groups:
Sharkhead Island: Considered sacred to the Coralax, due to the "Leviathan" being trapped in here. The Leviathan is apparently an Avatar, so to speak, of the Coralax God. Also, the island houses an enormous undersea cavern that is the only place to find Red Coral Crystals. These Crystals are considered to be precious gems.
The Coralax control the island secretly in almost every way. Coralax collect garbage and slag, then implant Red Coral in them to animate the Slag Golems.
Coralax have controlled the Freaks of the Island into being their lackeys. Freaks create distractions for the Coralax, and the Coralax enjoy their caves.
Coralax sell Red Coral to the Circle of Thorns in return for protection. The Circle controls Crash Cage, the daughter of the CEO of Cage Consortium. And since Crash is the CEOs only living relative, he does almost anything she asks him to do.
Coralax also occasionally use proxies to sell Coral to Arachnos in return for sanctioning the Caves underneath Sharkshead to be untampered.
Nerva: The ruins here comprise the main fortress to the City of Mu (Which there is only one of, if I can properly remember). The Circle now use the Thorn Tree to tap into the energies of Mu's Defense Grid (Which I can assume must be immensely powerful). Arachnos and Longbow vie for control of the Archipelago, although main fighting is based on the jungle island of Primeva. There, the Circle and Devouring Earth battle out as well. Crey also is investigating ruins in the area, and Arachnos is studying Portal Tech found in the Area.
St Martial: You got everything right... Except you're ignoring the Flop, parts of the Black Mariah, and The Hard Way. The Flop is a sector of St. Martial that is under attack from Freaks, Tsoo, Family, and possibly Rogue Elements (But I think this is a bug. It seems like Arachnos would deploy Spiderlings to the area. Also, they skitter around the feet of Arachnos soldiers without any conflict so I can assume it is a bug.). Crab Spiders have been deployed en masse to the area in order to keep peace.
Parts of the Black Mariah (Shipping center of St. Martial) have been attacked by Devouring Earth. And the sector known as the Hard Way is in devastation. Freaks have trashed the entire area and the Wailers dwell in the ruins. An ENORMOUS pile of flaming debris sits in the center of the sample of what could happen if the Freaks grow in power.
Coralax: As evidenced above, they play a massive role as the Puppeteer of the Sharkhead Isle theatre. They worship the god Merulina, which crashed into the oceans of the Atlantic millenia ago. From her, the Coralax evolved, and she was a living god to them. However, only a few hundred years ago, Merulina refused to speak to the Coralax for an unknown reason. This caused the fracturing of the Coralax Civilization into many parts. The main part of the seperatists believe that Human intervention caused Merulina's silence. These seperatists openly attack and infect humans and transform them into Coralax Hybrids. Though considered lower in their caste system than pure Coralax, the Hybrids play an important role as warriors.
Another seperatist faction is the Blood of the Black Stream. These Coralax are very mysterious and not much is known about them, apart that they have an Egyptian-like architecture, are very dark and underworld-ish, are based in the Nile area, and probably play puppetmaster to the Gadzul Oil Company.
The Coralax's Priests, Shapers, are zealots to Merulina. One particular Shaper, known as Calystix, has had many appearances. His first documented appearance was in Rome, around 55 AD. He had assembled a cult of followers in Rome, before Praetorians slaughtered every last member of his Cult for refusing to follow the Emperor as a God. Calystix apparently survived, and his last appearance was in a New Hampshire fishing village in 1904 before the village mysteriously was abandoned.
All Coralax can control water bursts of various temperatures. Their standard issue weapon is a very-suggestive looking club. They also have prominent psychic powers (which is how they are able to control Freaks and other people). Also, evidence shows that the Coralax are a likely candidate for the Epic Villain AT.
Carnival of Shadows: They want more Souls. Simple as that. They appear to run a legitimate "carnival" business, but they seem to be low on visitors, mainly because there doesn't seem to be an exit out of the Carnival.
That's all I can think of now. More to come if I think of anything I missed.