Anything that is a "profession" is what one depends on for his or her livelihood. So, if a boarder has enough sponsors to make a living w/o a day job or other means of income, then that would be a profession. Although there are variations of the definition. I guess it could go either way.
The WWA has an actualy definition for it... something to do with either having made it to the finals (aka top 8 or 10) in a pro comp, or having made more than $1,000 from prize money (i think that's the amount).