Some interesting stuff is on Sonic Team’s English SA2 page. It’s confirmed that the military is after Sonic because they think he’s Shadow, and that all the characters go to a space station named ARK that contains the “Eclipse Cannon.” Slightly surprising is tyhat Tails apparently is just as good with machinery as Robotnik, and Sonic and Knuckles are listed as “friends.” However, the big surprise is in Shadow’s profile. It says that he was built by “Pr.Gerald Robotonik.” If this isn’t a translation mistake, then Sonic Team is either using the English name for Eggman for another character, or the game could intro one of Robotnik’s relatives.
Source: Sonic Team