User blog comment:B214/Question and Answers 6/@comment-187.180.176.223-20190619153726/@comment-10330822-20190620011619

Also, reincarnated devils aren't allowed to found pillar houses. In fact, if a pureblood heir marries a reincarnated devil or human, their house automatically fall from status.

Ultimate-Class Devils found their territory, but nothing is stated about them being given full nobility. Because rank is based on strength, but the noble system is based on blood purity.