I was on a Canadian black bear hunt where I met a wealthy bear hunter from the US. This guy hunted all over for bears and showed me pictures with grizzlys, browns and even two polar bears. When the topic of gratuity came up, he said that he won't be tipping his guide because he is the outfitter. "You never tip the outfitter; he owns the operation". I' have heard this on more than one hunt.
I hunted bears with two brothers who owned the business and did everything from baiting, driving, recovery, skinning and butchering. We all tipped the two of them.
When it comes to tipping in camp; the biggest disparity in how much you should tip comes from tipping the cook. Everyone seems to have a vastly different opinion on that one.
While most hunters do tip. I've met a few who didn't. One guy told me, "I got exactly what I contracted for. Why would I voluntarily pay more?"