You guessed wrong. I want Diaco/Riley to hire the best coach they can get. Nebraska alum not a requirement. NFL not a requirement.
You are correct, however, that just because someone is an NFL coach, doesn't mean they can recruit and coach in college. I have no idea which ones (if any) would be a good fit at Nebraska. There certainly is a current NFL position coach that has the right combination of knowledge, charisma and energy that can recruit a four star safety to Lincoln, and coach them up once they're here. I couldn't tell you who that is, Mike Riley probably could.
I don't have a problem with an NFL DB coach if he can coach using college rules with respect to the use of hands. Sometimes the NFL types want to "prepare" their guys for the NFL to the detriment of the college team.