If they replace all the Jackson/Buxer tracks then it'll be Carnival Night, Ice Cap, Launch Base, the miniboss theme, Knuckles theme, the competition screen, and the credits theme that get replaced. But not simply lifted from the PC version, they have Jun Senoue on hand redoing the music and touching it up some.
However, as pointed out by
@TheCongressman, Katie said they can't use some "sounds" from the original, and that might mean they simply can't use certain samples (like MJ's woo's and stuff in the miniboss theme, for example), and they might be just replacing those vocal samples with other Genesis-accurate songs. Of course, Katie might've also meant to say "songs" and said "sounds" accidentally (she already took to twitter today to apologise for misspeaking and insinuating that Sonic Frontiers won't be at Summer Game Fest, so it's possible to goof a word during a stream),
but there's still a possibility we get the same songs just without the vocals.
Either way, we only have two weeks before we find out.