Information regarding the ‘Heroes OST’, here are links with some info on either the details or the artists:
Sonic Heroes Music Site
Jun-Senoue
For the First link: In Japanese, but talks about both the vocal track AND an upcoming OST for the in-game music.
For the Second: The Official Fansite for Sonicteam/Wave-Master’s top Composer.
Yet again—spiffy.
Source: Sonicteam