An owner could not make my April baseball draft (money league), so he handed his cheat sheet over to a friend and had him draft. From a commissioner’s prospective, I can assure you no one even considered getting upset over the owner calling for backup.
Not condoning the names that have been hurled at your co-worker, I agree that he has made himself the focal point of this dilemma. Hopefully, he is willing to provide a well thought out written argument of why your substitute would spoil the league. In the case that his argument strays distantly from a deductive path (99% chance) you should be in the clear
I love making my owner group support their obscure objections with "well thought out written arguments". So far, none of them have stepped up to the challenge, realizing that they were a little off-base with their comments.