As a few people have said above, there is no such thing as "reporting in" as an eligible receiver in college football. BUT, as people above have also said, the pass was backwards and in that case it doesn't matter what number you are wearing, it is legal.
Also, as some have said above, the officiating was not good...but it was at least partially a Big XII squad...so what would you expect.
They got that call wrong (and as someone else has said, it didn't really matter since NU scored. The bigger screw up on the part of the officials was on the kick return for a TD by Adoree Jackson. That TD, by rule, should have been disallowed. The rule says (this is not a quote, rather a paraphrase) that when a player does some sort of a celebration or act that brings attention to himself, that is unsportsmanlike conduct and that it should be penalized 15 yards from where the act began. In this case, Jackson sort of bounce stepped (to start his front flip) at about the two yard line. So the flag should have been thrown and the TD taken off the board. The ball should have been placed at the 16 or 17 yard line...first and ten USC.