I've used a hatchet to gut elk and deer several times and never touched the knife. A knife doesn't quite have the heft to split the rib cage on an elk but the hatchet does so quickly. It wasn't so easy as to make me want to do it sans blade every time, but I wouldn't balk if that's all I had. The only thing I use a saw for in the field is cutting the skull plate to pack out the antlers. All three go in the pack although if we're only after deer the hatchet could stay home. I never split the pelvis even on deer we take out whole. Rarely cut the butthole out either in the past 80 or so big game animals we've taken and never had an issue of any kind aside from people telling me it will ruin the meat even though it won't.
I will say that If I butchering a bison or elk back at the shop then a sawzall is handy to halve or quarter out for clients in a hurry. Other wise I prefer to take them apart at the joints at home or in the field if leaving bone in.
