I guess Delfino could complement House in some way, but I wouldn't say he's that good a passer. He's averaging 1.2 assists in his NBA career as well as .356 from the 3pt line.
He's a pretty decent defender as well, but I don't see why the Celtics would sign him at this point, considering they've already got Daniels locked, and perhaps want to give Walker and Giddens a go.
Secondly, he's getting paid a lot of money in Europe, while he'd only get the Vets minimum here. Not going to happen.