If they aren't cross server you might as well not put them in. You may get a couple groups that way for lvl 50 content but not for pre 50 content. Learn from WoW, when they put in the dungeon stones forget what the called them they were a flat out failure. You need the largest possible pool of players for something like this to work. If the community on the server was that vibrant and tight nit you wouldn't need the dungeon finder in the first place.