It is music, sure some of it is lame (every genre has it's garbage) but I call it music. I play a load of instruments and have been in several bands, there's not much difference between the traditional "music" we were playing, and the same music that is played live by rap artists. I have seen some rap acts where all they do is rap over pre-recorded music (like lip synching), but then again, some of the biggest acts that are supposed to be "real" music have been busted doing the same thing.
There are a lot of acts that use real instruments in their gigs and on their albums (N.E.R.D for example, The Fugees, OutKast, and on and on to the break of dawn.... haha ) so I'd say it's music, just because it's been overrun by lots of REALLY lame mainstream acts over the past few years doesn't mean it's not music, by some people's logic in these posts I could call a lot of other stuff "not music" as well.