The Lukes are interesting cases. Both very productive in college, but considered too slow and unathletic. I think Doc would cry if Danny gave him Harangody as yet another 6'8" center/pf. The other Luke is tall enough, however, to perhaps merit a peek.
I'd have no problem in picking Harangody with the #58. I think he'll be a limited and bellow average player who will work extremely hard to be as good as he can be, and will be able to help a team on those long February road trips when nobody else really feels like playing hard. He will shut down, say, Amare Stoudemire one of those nights simply by outworking him. He will be good for the coaches in practices.
If Ainge is planning on letting Powe walk and trading Scal at some point during the season and wants another reserve big for an extremely cheap price, it wouldn't hurt to give a look to Harangody.
I really don't know Nevill well; that's the only reason he made my roster, to allow me to watch him.
I like the Harangody you describe, but is that what we really need? We have had our share of fairly successful, undersized "bigs" in Gomes, then Powe and BBD. And hopefully we'll still have their services.
I think Danny needs to try to back up the forward spots with length and quickness. Someone who could stay with Rashard Lewis would not just defend Lewis, he'd create matchup headaches for just about everyone else. And someone big and quick could wear down our opponents to help out our starting forwards.