If you've got the license you can do whatever you want with any of it, so he's well within his rights to do what he likes. But I think most artists seem a bit more "respectful" - not to the artist, who I'm sure is best mates with the guy for wanting to use his song, but "respectful" to the art itself. You would normally use small sections of a song, or the track of a single instrument (Madonna - Hung Up On You, or whatever it was called, used four bars of one instrument in an Abba song). Not the entire thing with your one thing added over the top. If you or I did that, it would be karaoke, nothing more.
I'm all for doing things in different ways and not doing the same thing forever, but if I bought the rights to a Beatles song, and then copied the original track onto a CD but spoke the words "Beatles are insects" at the end of every line, it would be massively disrespectful to the original song, whether you've got the permission of the artist(s) or not. You're putting in no artistic effort, someone else (with talent) has written and performed the song, mixed it in a studio, added their own touches onto it, took weeks, possibly months over its perfection. And then you take sixty seconds on a Saturday to record "Beatles are insects" and stick it onto the end. You're legally covered, but hopefully, you'd get a complete panning from all of the music magazines etc... Although if Kanye West did it, I'm sure he'd get a couple of awards.
It's not a cover, it's not a remix, it's not a lot of effort really. It's cheap. Fair enough, he wrote some lyrics, but everything else was already done for him. I find it really repulsive; but then I never liked the guy anyway, nor 90% of the other artists out there at the moment, so, oh well.
