This I have to disagree on. I don't think it sounds like any of the Genesis Sonic games but especially in comparison to Sonic 4 or Generations, those are actually authentic Genesis sounds. It would certainly take me a bit to properly reverse-engineer the specific voices but I could probably replicate every single one of those tracks with the tools I use to make Genesis music. I think they used something legitimate to produce those songs, though it certainly wasn't anything related to the tools they used to make the songs for the old games like 20ish years ago. Could probably get a head start ripping voices from The Hybrid Front or something.
That said I don't think of the sound as particularly Sonic-like. If you wanted me to make a Sonic track I'd probably start by taking a couple basic sounds from the Sonic 3 "universal voice bank" and then experimenting from there. I mean this is actually what I've done to make Sonic-style music in the past and it's a pretty winning strategy -- slightly frustrating that they didn't do something similar.