I doubt this is very legal. After all, Disney still has the rights to Club Penguin and are actively using it in a mobile game.
A Private server like Toontown Rewritten is "okay" because Disney has actively abandoned the game/IP for now. If they were to suddenly pick it back up for a mobile game or something TTR would probably be in deep stuff.
Besides, didn't another Club Penguin private server get nuked a while ago for stuff-talking Disney and advertising their server on Twitter?