I think this is the definitive list:
Hudson, 24, who was presented with a No. 26 Celtic jersey, will play for the team in the Orlando Summer League next week. The Celtics team will also include J.R. Giddens, Gabe Pruitt, and Bill Walker, plus Nick Fazekas (Lyon Villeurbanne, France), Coby Karl (DKV Joventut, Spain), center-forward Mike Sweetney (formerly of the Chicago Bulls and New York Knicks), Robert Swift (Oklahoma City), and Darius Washington (Ural Great, Russia); and rookie free agents Chris Lofton (Mersin, Turkey), Bryan Mullins (Southern Illinois), Kevin Rogers (Baylor), and Bryce Taylor (Premiata Montegranaro, Italy).
For summer league, that's a fairly talented squad. Most of those players have shown that they can play at a high level. I doubt any of the non-Celtics get signed other than maybe Swift as deep bench depth, but I can see at least a couple of these guys making it on NBA rosters somewhere.