Oh nice, I didn't know FFXI had an explanation. That does sound like the same lore could definitely apply again. The GMs appear to be wearing "Judge's" gear that is similar to Templar gear, so maybe they're an order of knights originating from Ishgard perhaps.

Another thing I noticed before is that the area used for Mordian Gaol is the same area used in one of the cutscenes where Ascians are conversing with each other in a 2.0 main storyline cutscene. I'm guessing that's just because SE needed a spare area for the cutscene to take place in, but who knows, maybe GMs are in league with them lol. That could explain where they get their power to alter the fabric of reality to assist adventurer from.