User blog comment:B214/Volume 22 spoilers/@comment-30319856-20161025113305/@comment-9595671-20161027080448

Hmm... you know, I think her being Ajuka's queen can work. While those in a Devil's peerage are locked to their owners, Ajuka isn't participating in the tournament. So she and any of Ajuka's servants could be free to aid another participant if he gives them permission.

Yeah, and EX heavily implies Issei is not a Maou, just a celebrity. Serafall was able to visit class observations and didn't mention have any work to do despite being one of the Four Satan, and I think Sirzechs only had work due to the fact he's the Satan with the Lucifer name.