Well, I've tried this some time ago and then I've mind-controlled the aliens in question. Turned out the game doesn't even give the weapons to them, they didn't have them in their inventory. I didn't test the details of this behaviour because when I know the game only gives them one weapon, I saw no reason to question which one.
You can give the aliens a weapon, ammo and grenades, but that's about it. I've also tried giving them proximity grenades and while those do not disappear they are unable to use them.
I'm afraid this is the same as the aliens not being willing to use autofire if youre more than four steps away. We would need a new AI to be able to take advantage of the possibilities modding gives us. It would not have to be *that* smart but smarter that the current one and it would not behave as in the original game, so maybe we could suggest it as a new option. We have the Sneaky AI now and this one would be Trigger-happier AI