You as a producer should know this better than anyone. Would you call your instrumental albums "rap music"? Or for a better example, would you call "Endtroducing" an album in the "rap music" category? No. You can't. If you did it would be illogical. Why? Rap music implies that there are vocals in the music, but in instrumental hip hop there are no vocals. Instrumental rap, therefore, would be an oxymoron. So why label some of it hip hop and some of it rap? Why not just label it all under the blanket of hip hop music? It's less confusing and time consuming and, after all, that's how it was originally considering the first hip hop songs (before hip hop was on record) were instrumentals anyways.