Saunders said "The guy here", which implies the statistician stays at the location. This makes sense; I doubt the league pays for plane tickets to rotate the stats guys. Does the NBA pay the scorekeeper's salary, or does the team? I don't know. Either way, it is a hometown scorekeeper who works every game for the same team. Bias can be expected. I've seen nothing to indicate that the league hires them. The only statistics directly affecting the outcome of the game are score, timeouts and time on the clock. Probably the officials monitor those and no one cares overly about the rest.

Edit: LanierFan, thank you for finding that article. Very interesting read.