While I wouldn't mind getting Brewer, I don't think there's much of a chance that he has a steady role on the Celts unless we get an injury.
While I don't think there's a HUGE role for him, there should be a solid 12-15 (maybe a few more) minutes a game for him here. Bringing Brewer aboard might impact Delonte a bit, he'd probably play more-exclusively as the backup 1 and not as much backing up Ray.
Brewer can back up Pierce a bit, too, while Green is playing the 4. Might impact Baby's role a bit, too.
There's enough "hybrid" guys on the bench (Delonte being a 1/2, Green a 3/4, Baby being a 4/5) where I think they can find room to fit in Brewer.