Cloak of Fear and Invoke Panic

Yes, they would. It'll be crazy expensive to run it though. Invoke Panic is not kind to your blue bar.

Eh, even those won't really deal with it. If you get it perma (~200% +recharge, 95% +hold; ~1.14 end/sec), that's going to be like having a second Dark Regeneration eating away at your blue bar on top of having the more expensive CoF option rather than the much cheaper OG. Considering the end woes that */DA generally runs into without relying on heavy fear use, you're going to make it a lot worse just to be able to fear bosses.

Sadly my experience is No, having both a dark/dark stalk and a db/dark brute in PvP the fear almost never hits a player more importantly if I try to get a tech even the spiders are seldom effected by the fear I love that shield makes the build worth it in the cool factor but its a fairly useless end drain I am considering dropping it all together and take the build in another direction and hope for the best.

First off, punctuation is your friend. He gets sad when you ignore him to simply run on and on and on.

Secondly, PvP and PvE are completely different beasts, especially when you're talking about mez effects wherein magnitude means nothing (the OP's question is one of stacking magnitude), durations are all normalized (re: severely shortened), and the targets are actually equipped with significant countermeasures.

In PvP, CoF and Invoke Panic are most likely completely useless/redundant, but that's PvP. In PvE (where */DA tends to excel), either of the two will only take out minions but will stop anything not tougher than a boss when used together (and even those when the purple triangles are down). It's expensive, but it's remarkably effective, especially if you're using it within the context of a Scranktroller (Scrapper that acts like a Tanker and a Controller combined) build.