right now it's only really defined by the division you enter in at each event.
Generally speaking Div 2 (AM B) pay their way, and may get very minor sponsorship, consisting of discounts on guns paint and clothing based on the whole team buying the same thing.
Div 1 teams can get decent sponsorship for paint (mostly free or atleast a killer rate), and usually good deals on guns and clothing.
Pro teams almost never pay for paint, guns or entry fees, and are ususually subsudised for travel and hotels. Some pro teams pay them selves from their winnings, and a lot of pros work for their sponsors.
In the states there are now true pros, most of the NXL teams (i'd classify them as super pro) pay their players, and some of the bigger named players like Chris Lasoya make a good living playing paintball, (although i imagine a seriuos part of his income comes from promoting Draxxus too). I don't know of any pros in England who are paid to play, and i'd imagine it'll be a few years before there are any true pros over here...