i often get stinky tofu from 素食 places and i'd suppose they as well as non-veg vendors source it from the same place.
i'm not very familiar with zhejiang-style, and while i've eaten kilos of changsha-style, most of it has been the cheapest type of street food, mass produced, and i can't imagine they would use expensive ingredients like meat just to marinate a 6-kuai street food (or ever stranger, milk, liquid milk being a specialty drink you have to go to like a walmart to buy)
though when i visited changsha, the stinky tofu they served there sometimes was topped with mince. wtf.
guizhou/yunnan types on the other hand seem like descended from 毛豆腐 rather than something fermented in some animalesque brine. they're wet/sticky on the inside (before cooking) and seem to be just fermented tofu, not soaked/marinated.
taiwanese style is mostly vegan, but sometimes they make a disgusting soup out of intestines and stinky tofu, which is actually properly stinky because it smells like literal shit, while the tofu itself normally is just a bit cheesy
regards, a tofu enjoyer
this is what happens to regular people in the Culture universe, it's pretty much there in the books