Is it possible to have Music on the app not from Itunes or the Music Kit?

Planning to create a Music Game App similar to Guitar Hero kind of, and I am planning to use songs from beginner producers (They don't have any Publishers or Distributors). If I get their legal concent through a contract to use their songs, does Apple allow to have Music that is not from Itunes if I get the legal license from the producer to use their songs in my app?

Will apple allow songs that don't have Publishers or Distributors, or in the App review stage they will flag it and cause an issue for me?