The main reason I don't feed rats is because my two rat-eaters are not fully converted, and I hate being stuck with live rodents, I don't have time to care for them. When I feed live, I feed mice because I know for a fact that they'll get eaten.
This is the first time any of my snakes have been bitten, so I don't have much to compare to, but I have worked with rodents in the past. I've been bitten by countless mice, but never by a rat.
But then again, you have to consider that mice aren't capable of much damage, while rats are. I think that, no matter how friendly the animal is, if it's being constricted by a snake, it's going to bite if it can.
I don't pre-kill either, simply because, as I've said before, I've worked with rodents and can't find the will in me to bonk one.