If you had two cultures, one from hip-hop genera, the other from hard rock genera...?

Your question is kind of odd but music comes out of race, race does not come out of music, the function and dysfuction of every races is what creates their music. The environment affects the music its not the music that creates the environment. As each group developes separately their music grows separately as well. I think you are perceiving it backwards or assuming it works in the reverse.