Probably a similar % to that of the number of professional footballers (soccer players).
There about about 15 senior football teams in my town. One is "semi-professional", but in reality only a handful of their best players get a few quid a month and they have full time jobs. The rest is completely amateur where players pay the club in order to play.
The nearest professional club is about 15 miles away where the full squad earn a living playing football full time, but they're hardly living the life of luxury. The majority of the working population of that town are probably earning a lot more than they are.
Then about 25 miles away is the closest Premier League team, where even players that struggle to get into the first team squad regularly are paid tens of thousands of pounds a week.
How many amateur teams are there between my town and there? 100's maybe even 1000's. Those are your losing poker players.
How many semi-pro teams are there? Maybe 15? They are your decent recs/regs who win a bit, maybe make a half decent side income.
How many pro teams are there? Two, possibly 3. They are your grinders who live off poker, but you don't hear too much about very often.
How many Premier League teams are there? One. This is your elite, high rolling superstar.
So, that was just a very long winded way of saying somewhere in the region of less than 1% are actually a living from playing poker.