I'm not entirely sure, having not reviewed the MLBPA contract (I'm a criminal defense lawyer, so contract law understanding is essentially confined to law school for me). I also haven't seen Gonzalez' contract or any other subsequently signed player participant's contract. But it seems to me that the contracts the players subsequently signed could be voided as they were bargained for based partially on fraudulent statistical data. Hell, Gonzalez has a career season, admits to cheating, and it seems to me the Twins should have a right to recovery.
Any contract attorneys on this site able to chime in?
I'm not a lawyer, nor do I play one on TV.
But my understanding is that the contracts are pretty specific, and can only be voided if a team can prove the player engaged in specifically prohibited activities -- like the Yankees did with Aaron Boone, when he injured himself in a basketball game after his contract forbade him from playing basketball.
There's also something called the "morals clause" and teams have tried to use this against players who get in legal trouble (recall Sidney Ponson punching a judge!). But generally, teams haven't been too successful at that, because it's much more of a judgement call -- at best, they maybe save a couple mil in a settlement with the player to terminate the contract.
If there was any case to be made to void the deal of a player who cheated and put up "fraudulent" statistics, I'm sure it would have happened a million times over by now. Recall how Ervin Santana was suspended for PEDs before he even threw a single pitch on his Twins FA contract.