This is a lot more debatable.
In the case of a trap, the lemming is dead either way. The only difference it makes is whether one could perhaps set up a situation where they allow one lemming to pass a trap, by direct-dropping a lemming onto it from a height it couldn't survive the fall. Arguably, the traps detect the presence of a lemming (and go off) and not what the lemming is doing, unlike an exit where the lemming itself jumps into the exit.
In the case of a teleporter, the lemming should come out the other side and splat anyway. Once again, they're detecting the presence of a lemming, and the lemming dies either way. (If it does not splat at the other side, this is a bug.)
I'd like to get more opinions on this one before making any decision though.