How often will a center shoot a 3 point shot in the triangle offence? I have a player I am playing at center who is High-High in PE as well as LP and want to know if he develops that outside game if he will be able to use it at the center position in my offense....

It depends on his PER rating and the 3 point setting... in extreme cases you can see post guys who take a large percentage of their shots from outside the arc.  I suspect it's lower than for guards, but it's not outside the realm of possibility that given the same ratings and 3 pt settings it's actually the same...  It would still appear as if the post was taking a smaller proportion of 3s as a result of putbacks.

This doesn't directly answer your question but...

Years ago in D2 at one of the Alaska schools I spent years (7?) trying an all 3 point shooting team. It appeared to me something in the code worked against bigs MAKING 3's. Even with very high PER the power forwards were eh, so so, by their junior years. Centers never could make them even at a barely acceptable rate. These results were during the regular season when most teams played "0" positioning. 

Not sure if this was just my usual ineptitude but those were my results.

I had a guy that I played mostly at center in D2. He had 56 SPD, 67 PER, and 30 BH. He shot 44/99 during his career (mostly during his SR. year) from behind the arc. I think I set him at +1, so it is possible for centers to shoot some 3's and at a decent rate. This was in a motion offense, so it might be different in a triangle.

At least for power forwards, I have had plenty that shot a significant number at a 40+ percent rate.

(Significant number being somewhere between two and four attempts a game.). I haven't had a center to do that, but mainly because when I get a post capable guy like that, I usually end up putting him at small forward or power forward depending on his other numbers.