Youtube pulled the video down but I managed to download it before Activision made them do it, here is the link
http://rapidshare.de/files/48693238/video2.mp4.html
Guitar Hero 5 apparently can play the same DLC and let you import songs from Band hero (the pop equivalent of Rockband), that also means that any characters in Guitar hero 5 can be used to sing those songs.
It was bad enough in Guitar Hero 5 seeing seeing Kurt and Johnny rap to the Beasty Boys, but this takes the piss! 
No wonder Courtney Love wants to sue Activision, still pretty funny though (provided your not related to Johnny Cash or Kurt Cobain)