I havent played grav, but it also has slows on some of its control powers which can really help against resistant targets. Certainly a pain in the backside when a grav troller comes for me.
As well as fear. Levitate and TK are also big hitters for a pvp mind dom imo. The lack of a pet doesnt bother me personally, but I'm not all that keen on pets that do there own thing anyway.
Plant rocks for the confuse power, I havent got one high enough to try creepers yet, looking forward to it though 
Trouble is, the plant holds only work on the ground and seem a little bit buggy against leaping opponents.
BTW. drain psyche recovers a LOT of endurance, but lasts a very short time, easily enough time to build up domination though. The health recovery from drain psyche doesnt impress me very much.
Psi dart is great for building domination quickly. Also try getting aid self into your build.
Whatever set you go for, dont expect an easy ride in pvp, my own dom didnt start to feel all that useful in the zones until about level 40.
My MA IDs:
Fiend Space: 211464
Mind has TK which boosts dom survivability in duels tremendously. Plus mind has good mezzes(spam dominate, mesmerize) overall. I have no experience from Plant so cant say. I think Grav is ok, but dunno if singularity is better than TK
my experience in RV (only RV event) is that my fire/fire got the best prestige of all the doms i tested: 20 prestige in 1 hour.
Think about the power of the imps, and not in control the enemy and hope he will be mezzed 20 secs, that is the time u should need to kill anything except a squishie.
Thats my point of view.
I myself have a Plant/Thorns Dominator, on which I PvP quite a bit on occasion. One of my greatest strengths in PvP are IMO:
[*] Seeds of Confusion
[*] Carrion Creepers
[*] Toxic DoT
[*] KB
As a Dominator in PvP, you will necessarily need these:
Acrobatics (through Leaping pool)
Aid Self (Medicine)
Stamina (You can get along with /Psi unless you tend to miss alot
Hasten (Speed) is optional, but I use it to get Domination back off faster and hold much, much better and burn their BFs.
As a Plant Dominator you can use Carrion Creepers and Seeds to a great effect of self defense, as the Seeds make the enemy confused, and Carrion Creepers create more targets! It's very hard to aim for the Dominator jumping around using Ripper to get through your mezprotection, and later on will achieve Domination, which is fun. 
While they're suppressed, use as much KB powers as you can because this negates them using their own attacks in rapid fire, eg. Blasters. Toxic DoT helps me to keep an enemy not using Aid Self too easily and will interrupt any other interruptable moves like Snipes.
Aid Self is crucial because of the fact that you have really bad defense in PvP, while your enemy can easily destroy you in 3 hits, you need alot more time, using your surroundings carefully you can keep your enemy in a -jump field like Carrion Creepers or Ice Slick.
And if you lose against FoTMs, it's just the hard fact that most FoTMs are just powerful enough to beat Doms (Spines/ Scrappers, Ice/EM or Elec Blasters, most Controllers, Rad/Psi Defenders, Stalkers... etc.)
And for your question, Spirit Tree gives 200% more regen while unenhanced, and Drain Psyche gives 100% more regen each target it hits. So, you can get a few percents from the gap by slotting your Spirit Tree with 3 heals (close to 400% more regen, 500% is the gap) you can use Drain Psyche to achieve that gap. The heavy -rechg on some /Psi powers will make regeneration even more important, as they will hit less and you will heal more
the only thing i am sure is taht it would be a **/psy
after that i must admit i have several primary in mind.
plant: i would like to see how spirit three+drain psyche and the Aoe of psy while in a Carrion Creepers would work ^^'
mind: as it is the control masta and fear is cool in PvP
grav: i heard about and experienced the annoying Singularity.very strong
so,
is a set worht it for it's pet only?(grav)
does a multitude of control negate the lack of a pet(mind)
would plant be usefull in PvP? (necessity to be on floor for some power)
quid??