Meat is meat. It ain't much different. No, I've not actually had yak meat. I have had muskox.. pretty close

Meat centric cultures (like inuit) don't get scurvey because they don't have the western habit of eating nothing but muscle tissue, the eat innards too. lots of varied stuff in there.

And the old guys that ate mostly meat didn't eat *all* meat. you hear a lot of talk of pemmican and the like (which is a lot of berries with meat). etc - there were foraged wild edibles in there too - and a good solid rosehip of a nice wild rose up here is supposed to have as much vitamin C as an orange. spruce tea, etc. all these are vitamin sources.

I don't think there'd be any magic to yak meat any more than eating a moose, buffalo, elk, muskox, or beef steak...