Yes.  Actually, you can even have a player sold before the game begins as long as it's after the lineups are locked in, which is 15 minutes before the game.  So if your player sells at 7:50 and your game starts at 8:00, the player will actually still play.
Assuming, of course, the game calculates on time - if there's a delay and it starts after the transfer is processed, that would be most unfortunate. Usually that's not a problem but generally game 3 of a finals series is not the time to be open to risk. 
