With rap the musical element to it does add an addition to the impact. As does your voice which concedes with your theory, although since its art you can do what you please in it. The line between rap spoken word and poetry are all very very thin, I just choose to call anything that's intended as rap, rap. If you write a rap song and have yet to, or have no plans to record it its still a rap song to me. That's just me though. It's a very suggective thing.