I haven't played the DLC in a while, but if I had to guess, I think it's based on the OT. I think if you had a bunch of kubfu and only one had your OT, that would be the only one allowed in the tower. However, Bulbapedia says the player is allowed in the tower if kubfu is the only Pokemon in the party, but if kubfu isn't in your party or boxes, you will be let in and use any Pokemon, so you can probably rock a full kubfu party that way. I'm not sure how the game interacts with kubfu once you go in with anything and then bring kubfu back to your game though.
I may be remembering some details wrong but I do remember having a kubfu from another file that couldn't participate in the current file's sightseeing activities after the current file's kubfu evolved, which leads me to believe kubfu being let into the towers is OT based.
