Between Zeller, Anthony, Fav and potentially Colton . .. it's hard to say the Celtics don't have a "true center". All 4 of these guys play the 5, and nothing else.
Maybe none are All-Star caliber centers, but they are centers. They aren't undersized PFs trying to play center (a la Bass, Sully, Hump and KO).
I think just the fact that we have some 5's this season will help. Once Fav went down last year, we really did not have a true center.