[robg adds: The oversight here seems to be the lack of a Music Video entry in the Library section. I have a bunch of music videos on my hard drive, so I tried importing a couple. They showed in the Movies library on initial import. When I set the Video Kind to Music Video, though, they migrated into the Music library. Yes, you can use a smart playlist (Kind - is - Music Video), but I'd rather not have my videos intermingled with my music. So for now, I've left them all as Movies.
I also noticed that you can't change the Video Kind for music videos from the store -- at least, I don't think you can. I've never purchased a music video from the store, but I have a freebie that I downloaded. In its Get Info window, the Video Kind pop-up is grayed out, so it's permanently marked as a Music Video.]

