<3M2K, Azen, Chillin, Ninjalink, Ally, Atomsk, Futile, Reflex, Inui, etc could probably do this.
Honestly, if I wasn't going to college, with a bit of startup capital, if I went out of my way to enter all the tournaments in the surrounding states, I probably could live off of the money, although it wouldn't be comfortable.
I'd rather get my Bachelor's Degree in Psychology and become a counselor than that, though.
I think that most people look at "pro Brawl players" as the famous players known for their character; Futile is synonymous with Wario. I've never considered myself "pro", but a fair amount of people appear to think so, so I guess that would be a good, generally-accepted definition for "pro".