It should work, but that's not a very good way to do it, since it will be reloaded every time you switch rooms. If this gui has, for example, character info, you will have to give it that info again every time you switch rooms.
I suggest you have a "World" scene that contains the gui scene and the current room scene. You could have both be children of /root, but that would make things more of a pain to deal with, since it's not really under your control.