I'd heard that there were indeed poker sites that accept Bitcoin. ... There's obviously https://betco.in/
which is actually a bitcoin poker room (bets are denominated in BTC) and a few others like that, but that's a different deal than just using BTC as an initial funding mechanism, which is what the major poker sites would do.
Does Pokerstars allow player-to-player transfers? If so, then someone who already has some funds in Pokerstars could sell their chips privately for BTC.