Which leads me to wonder... do vegans smell like herbivores to the predators?
I'm not certain how much sarcasm there is in your question, if any, but diet and body scent are directly related. One of the first things an American traveling to Korea will notice about Koreans, especially in close proximity like an elevator) is an odor of garlic, pepper and rice. Koreans think most Americans smell like spoiled meat or milk.
Humans on average, have one square inch of scent receptor tissue with about 5 million scent receptor cells. A large canid like a wolf will have upwards of six square inches with 150 million scent receptor cells. There is no doubt in my mind that a wolf could differentiate between a vegetarian and a normal person.