Maybe with copious of protein powder, expensive vitamins/supplements, and probably a bit of T thrown in there for good measure... and they probably still don't do as well as they could. I'm very skeptical that someone could go vegan and see reasonable gains, and even so, it's probably expensive as hell.
It's not all that practical IMO. I mean, if you want to dirty bulk, you can't even eat pizza as a vegan? What the shit is that?