http://espn.go.com/blog/bigten/post/_/id/26078/nebraska-loses-aau-status
Nebraska got voted out of the AAU in early 2011. Nebraska knew for years that this was a possibility and that they were at risk. Nebraska officially joined the B1G in July of that year. Notre Dame has been invited to the Big Ten before, obviously the AAU thing doesn't matter to them when they have a non-member, and have tried on multiple occasions to get another(ND) .