I was wondering if the suppression ability and its accuracy reduction works on the Mind control abilities, or any psi abilities for that matter, of the aliens?

Not sure, but don't think so from my own experience.

Doesn't every ranged attack in the game have to "roll" to hit?

Since MC is a ranged attack I assume it would use aim?

I won't say for sure, but my experience with psionics is that sight or range or anything like that doesn't matter at all, it's just all about will.

@Ares42 said:

I won't say for sure, but my experience with psionics is that sight or range or anything like that doesn't matter at all, it's just all about will.

You definitely have to have line of sight on the target it to work.

Percentages are, however, determined by will and nothing else - you're right about that.

@Terramagi: ofc, I was thinking about half/full-cover etc.