I'm not sure how this would work. When the DM loads a level, it automatically transports the players to the level, as it should. I guess if the DMs were always in the same level at the same time, that could be okay. I think it would just be too complicated to make it work and I am not sure it's even necessary.

GMAddon1: Adds almost every single monster and NPC from the main campaign into GM mode, plus a few large custom maps to use in GM mode.