Ok, we'll be adding vegan in the next release! Your wish is my command
If you can do it as well as your other categories and market it as such you will definitely become a "must have". There is an app for happycow but it requires a lot of sorting to find a) businesses that are still open (as in both not shut down and currently open for business) and b) worth dining at!
Not yet, but I'll take this as a vote for it
seconding support for a vegan category
Need this as well - it's the main reason I use Yelp.