Thanks. I wasn't using the latest PkHeX (go figure). I figured out that the version I was using improperly saved Pokemon's Memories, and that made my Vigoroth Illegal. After updating the app and removing the 'Residence' data, Vigoroth is now finally legal for the Battle Maison! (Actually, the reason why she wasn't being accepted was because she had a Kee Berry, just like my Blissey, and I can't have 2 of the same item. I couldn't read because I had just woke up when I posted this.