There are plenty of pizza places that serve hot subs or calzones. Having a wine bar that also has whiskey isn't unusual. An item not being in the name of the restaurant is fine. But "vegan" isn't really a food item, it's a cultural/religious choice. It'd be like having a baconator as an option at a Jewish deli: Technically, nothing says they can't, it just seems VERY out of place.
Can you call yourself a steakhouse and serve salads?
Sure, unless your name is 'Only Steaks and No Salads', although people that eat steak would be less inclined to care about the presence of salads.
There are plenty of pizza places that serve hot subs or calzones. Having a wine bar that also has whiskey isn't unusual. An item not being in the name of the restaurant is fine. But "vegan" isn't really a food item, it's a cultural/religious choice. It'd be like having a baconator as an option at a Jewish deli: Technically, nothing says they can't, it just seems VERY out of place.