I think everyone should build an entry and exit hall into their room, it'll smooth the process over. That is unless they want the player to be teleported in.
Maybe, each submitted map just needs an entry hallway? This way, the next entries' entrance will serve as the previous maps exit hallway?
If the map's being teleported to and from, then obviously a hallway wouldn't be needed.
Alternative to having the requirement of a connecting hallway, we could just have a standard themed/textured hallway that would connect every entry, thereby putting more focus on the rooms than anything else, though this may get a tad repetitive.. (you could spice up each of these hallways by having signs saying "room 6 this way" and change the music, lighting, etc..)
These are all just ideas. I'm game for whatever is decided! =)