Everything I have seen indicates the Clippers were asked.
In the end, according to League sources, the NBA gave the Clippers the choice to let McCollum play, Doc Rivers declined.
Trail Blazers' blunder, Doc Rivers' gamesmanship send CJ McCollum to inactive list
If the Clippers were asked and said no, then that's a bitch move by the Clippers, imo. You should want to beat a team at full strength. I'd say the same if it were Byron and the Lakers.
However, end of the day, it's the Blazers own fault for making the mistake in the first place and putting it in the opponents hands. I'll bet their coach looks at the lineup card a lot closer from now on.
I do agree though, that the Clippers shouldn't have been put in that position. If it's a rule, enforce the damn rule or get rid of it. Don't put the opposing team in that position.