mechmouse: Took me a while to figure that one out... I suppose hiding someone in a wardrobe in the blistering heat of a desert would do that.
ast486: I hope that's wrong.
Bad news: some missions have an optional "do not kill" objective. As soon as you dump a body, that objective automatically fails. That's how I know that dumping bodies is lethal (I had dumped the body in some clothes drawer).
I'm not too sure about dumping bodies in cars, however.
Good news: you don't need to hide bodies in this game anyway. Patrol routes are pretty much fixed and very limited. Enemies almost never change their route. At most, they'll stay in the same place forever, and only move if you get closer or reach a certain location.