It's both. Art reflects and influences society. (I won't get into whether rap deserves to be called art/music or not; y'all know what I mean.)
For now I'll set aside the effects of mere music on the mind, and focus on lyrics. If you hear or say something enough, it cannot but affect you, consciously or not.
Rap tends to focus the mind on violence, crime, and immorality. Hearing it may not make one a criminal, but again, it's going to have an effect.
Great answer. I agree. I don't believe anyone can stay with God if they are constantly singing Rap lyrics.