Could a character like brother voodoo free action mind control an opponents figure to summon an ID character from my own sideline?

There's nothing on the ID card that says you can't, so I'm guessing yes.

I submitted the question to wkrf just to double check

What happens to the summoned fig when the MC'ed fig is no longer friendly to your team?

Nothing...

It becomes friendly to your opponent for 1 action.

Not to be snarky, but the only way that an ID Character is any different from a regular figure is how they enter and leave the game. As long as one of the 3 conditions doesn't apply ((a) at the beginning of your next turn, (b) if it's not within 5 squares of the chosen character, or (c) if it is removed from the map by another game effect), then they are treated just like any other figure on a team, including that they can be MC'd by an opponent (or friendly if you have friendly MC) and they can be KO'd (for additional victory points, mind you).