PER's not a particularly good measurement for anything, though, and it's certainly not the one I would reach for to evaluate a player as shot-adverse as Rondo, since PER rewards shooting a lot (even if you miss, you'll still rate higher than if you didn't shoot at all).
For example, you can't seriously think that Isaiah Thomas and JJ Barea deserve to be in the conversation for the top 6 point guards in the league (they're ranked third and sixth, respectively), by PER.
You don't really think Dennis Schroeder (ranked 12) is a better point guard than John Wall (rank 13), do you?
and so on.