I actually read a study somewhere (I'll try to dig up the source and see if I can find it) that showed survey results saying that more doctors were athiests than most professions. I'm not sure whether it's a reaction to the awful things you see as a doctor, or whether it's the scientific, objective mindset, but there are certainly a fair amount of agnostics and athiests in medicine.
For those doctors that do believe in a god, I'm not sure whether or not you can really quantify faith by saying they believe more or less than someone else.