Portland was assessed a technical foul after the fact, but because the officials didn't notice the 6th man until after the basket was made, they couldn't waive it off (those new fangled scoreboards!). A call was also made to the league office during the stoppage, but they apparently shrugged and said they didn't know what to do.
From Doc Rivers: "They said you couldn't correct the play, which I still disagree with. But the problem was that we called around, we called the league, and they didn't have the answer, either. It is what it is. There is nothing we can do about it."
Awesome. David Stern must be so proud.