I think people who are trying to collude normally try and at least make the trade just look like a bad trade as opposed to an overly lopsided trade like this one. It is either the most obvious collusion in the history of fantasy baseball or just a dumb trade where one owner is way overpaying for Miggy, he is completely gutting his team imo. However I think while vetoes should primarily be only used in cases of collusion, this trade is an exception since you are saving team B owner from himself by vetoing the trade. I would definitely veto.
I am nearly 100% no veto, but this trade is an abomination. I think you might have to send a message that not all trades go through, especially in a non-keeper, and that this is just not gonna fly. I'd have to veto, there is really no justification for this deal.