You don't get banned or disallowed from Festival Plaza for having Hacked Pokemon; the only things you'd get banned from is Tournaments only if you participate with said hacked Pokemon and the game recognizes the hacked Pokemon as Hacked. Also, what KRLW said is 100% correct. All the Pokemon/Items you got from that person are hacked in; items are easy to generate without having the game detect it, and hacked Pokemon can be traded as long as they are possible to have within the game's code, which is pretty easy to do. Hacked Pokemon don't have to have impossible moves or abilities, etc., and are often generated with legal stats and moves so that they can be traded. :P