Of course you can rebound on the perimeter. Jason Kidd has made a Hall of Fame career out of it. For comparison's sake, let's look at other Spurs players' per 36 minute career rebounding rate.
George Hill - 4.0
Manu Ginobili - 5.2
Richard Jefferson - 5.3
Tony Parker - 3.4
Roger Mason - 3.3
This is why I consider Mason a poor rebounder.
As a defender, I consider Mason to be the poorest on the team. I base this on his adjusted plus/minus defensive rating which you can see for yourself at basketballvalue.com. I've made the argument many times on this site that Bonner is an average NBA defender for his position but because he's an unathletic white guy, he's constantly underrated. RJ is actually a much-improved defender this year but we'll have to wait and see if it holds up in the long run.
Finally, I don't see any way you can consider Mason a better player than Bonner. I've already mentioned the defense. On top of that, per 36 minutes Bonner is averaging more points, rebounds, and less turnovers this year. Bonner is shooting .451 from 3 compared to Mason's .349 (below his career average but he's never been as accurate as Bonner) and factor in the value Bonner brings to the rest of the offense by drawing an opposing big out to the perimeter to open up the paint for Tim and Tony and there is really no comparison. Mason is making almost $3.8M this year and Bonner only $3.2M and I'd be surprised to see Mason on the Spurs next year if he expects any sort of pay raise.