This WAS the last round. It had the benefit of forcing the GMs to fight.

Your tournament was short one round.

If the justification was to force GM's to fight , would you have rejected a
short draw with a double forfeit of both GMs ala Jarecki? Moving players
around in the last round to force "fights" is a bad idea. I did this once or
twice for class players in Opens who wanted to play each other for the class
prize. "Blood" was promised. Instead of the "promised fights" for class
prizes, I usually got lots of quick draws. I get more "fights" if the class
players have to play up or down the last round. Also you denied two other
players a chance to play a GM. Better just to pair top down and let the cards
lie where they fall.

Of course, one of the GMs just stormed out and forfeited. He's no longer
welcome in our tournaments.

No excuse for bad behavior but it was a bad pairing. If I was you, I'd think
about repairing this relationshp (if possible) rather than banning someone
(which is how I read "no longer welcomed").

Not the end of the world; that's why us TD's get "The Power Bucks".