I don't see the other teams need for a closer. He has 3 good closers, and he won't finish last in saves, unless there are only 6 teams in the league.
I don't veto trades unless I think people are cheating, or I think the trade is so lopsided, it'll compromise the integrity of the league. I don't think it falls into the latter, I can't comment on the former though. I do think the other guy is fine with his closers.