So turns out the Gamecentre App for boxee is pretty useless right now. The app has no way of knowing if the stream is live or not and thus it just starts playing from the beginning of the gamecentre stream.
So if the gamecentre stream starts 2 hours before the game with the "this game will start soon" screen, then boxee will just play 2 hours of "this game will start soon" even if it's well into the game.
More info here:
http://forums.boxee.tv/showthread.php?t=43370&page=11
On the plus side you can still view gamecentre in the Boxee Box webbrowser app, so all is not lost. But the native app is worthless in it's current form. Not sure if the folks with an Apple TV are having better luck.