While playing Mass Effect 3 on PS3 (I have a copy for PC too), I noticed that Adrenaline rush and Cloak don't really work for me on MP.
Adrenaline Rush gives you the stats boost despite it not slowing time, probably because that would be difficult to do in multiplayer:
This answer to another question seems to indicate that cloaking works. Can you be more specific about your problem?
Edit: I agree with yx. that you're probably just expecting the wrong thing here; as he says, Cloak just makes you harder to target, not impossible to target.