ACID music studio comes with a cd full of samples and stuff, and I swear that I recognised at least three samples from sonic in there. Green Hill zone and casino nights zone for definate.
Well, ALL songs are copyrighted by their authors (in this case: the remixers).
The only ones who COULD be blamed for making illegal stuff are the remixers. But companies don't really care - since playing remixes doesn't rip them off their money. They want to sell the games or the OSTs (if they even want to sell them), not some remixes.