I have a D1 Center who has great REB, SB, and LP, with 75 DEF.  Problem is his ATH is only 58.  He put up pretty solid numbers last season, asides from fouling a lot.  How much does his 58 ATH hold him back?  Can he still be a worthwhile contributor?  Would he be less of a liability at C or PF?(I play mostly 3-2 zone)

Oddly enough, there's an answer to that last question.   In a 3-2 zone, defensively, it is indifferent whether played at PF or C.   Those two positions are averaged for defensive purposes in a 3-2, but not so for a 2-3.  He may not be a rebounding liability, in fact.

On the other hand, poor ATH & mediocre DEF ratings will make your post defense worse even though he has good SB & REB (he will be assigned most of the fouls, but will pick up his share of rebs & blks).   I would avoid starting him, but, in a 3-2, he could come off the bench at both positions.

I was considering starting him at PF and running a 2-3, and starting David Walls to negate the ATH and DEF hit from Blackmore.  Probably won't do it though, because of Walls' low SPD.

This conversation isn't connecting up.  Try reading from this post onward in this thread about zone.  Looking at your team, I thought you were planning to run out Blackmore & Crawford as the posts in a 3-2.  That seems like a reasonable idea and might hide his weaknesses (although not as well as bringing him off the bench).

As for being a PF in a 2-3, I dunno, who's the C in that situation?  If you're planning to start Blackmore, then I'd rather see him in a 3-2 as a way to hide him.  

I should have clarified - I meant I was considering starting Walls at SF in a 2-3, and starting Blackmore at PF.  Since the SF and PF are grouped together in a 2-3, I felt that Walls and Blackmore complimented one another's deficiencies pretty well.

I decided not to do this, as I didn't have enough confidence in Crawford's rebounding as a C in 2-3.  I will probably use Blackmore as the backup C, and start a freshman I have coming in that I'm pretty high on.