Can't say I've ever seen that happen. Enemies would die in the same way then, correct? Hehe, imagine a room with arch-viles and arachnos with a self-referential teleporter. I could only hope for that.
I guess the lesson is, don't take teleporters unless you absolutely need to, or you see an enemy go in or come out the other side.
Ah, what if an enemy teleports on top of you? Always wondered about that. Been too afraid to try it out. Spider's Lair would be the best place, but I don't want to die that far into the game.