After listening to 5 seconds of TI, and knowing Dre's history of ghostwriters, I think this could very well be the cover vocals for him to eventually rap. At least TI's part, as it is very methodically different from TI's usual work. It's hard though to say Nas' lyrics are tuned for Dre in the same way.
Maybe the track was meant to be Dr. Dre Feat. Nas, it actually sounds tight the way it is though, btw who is that rapping on the hook? I can't quite figure it out, some peeps on allhiphop.com think it's LL, I don't so though