I don't see how the stats support your claim. The average PER always hovers around 15. His oppPER indicates that he'll be an average or marginally above average defender at best.
+/- is one of the most useless stats in basketball. It's more dependent on the quality of a player's teammates than any other stat.3) over one game? Definitely not. Over the course of 66 games? I think it certainly is relevant and, yes, does translate to wins with sufficient minutes played per game.
Case in point: Josh Harrellson has a 8.5 +/-