You are very right on the O glass. The fact he's there and he's a handful rebounding requires the other team to have more than a couple of guys to go for the board, no. 1 to box him out, no. 2 to grab the board or preventing a tip in. All of that helps the Spurs transition defense I think.
Ultimately, yes he has sacrificed his game for the sake of the team. He's getting far too many jumpshots too, from the top and all over, like you say to space out. Occasionally they go to him in a post up, I think only if Pop has noticed that the team is ignoring him too much and he's starting to loose his aggressiveness.