I have a player with a PER rating of 100, so I set him at +2 on his 3pt frequency. Through 5 games he is 18-37 from beyond the arc, and 18-39 overall. Is it pretty standard for a guy set at +2 to take nearly all of his shots from out there, or does it vary depending on their other attributes?

Depends on other attributes as well, and specifically depends primarily on a combination of your setting and the ratio of the players' perimeter and low post ratings.  Since the player in question has 100 PER and only 11 LP, he'll tend to take a lot of 3s on any setting except maybe -2.  Put him on a +2 and you'll find that nearly all of his shots will continue to come from behind the arc all season.  If you took an SF with 60 of each and gave him a +2 he might take as few as 60 or 65% of his shots from behind the arc.  Still quite a few, but not the same as what you get here.

Between the +2 and his LP rating being only 11, most of his shots will probably be from behind the arc. His rebound rating of 3 also reduces the chances that he'll be shooting from in close on put-back opportunities. 

yes, as mentioned, with the +2 and the high ratio per:lp he would be expected to take most of his shots from deep. Since he's hitting 48.6% from 3 pt (and 0% from 2 ) I'd let him keep chucking...

ETA: I'd up his distro a little and see if he can handle it and maintain the percentage...