Did the USADA get to see/use the DOJ evidence that was collated before some random senator/govenor closed the case unilaterally?
Quite why a politician should have any power over a criminal investigation is beyond me. Although I guess it's worked for Berlusconi for a long time now!
Just to be clear, the DOJ matter was being supervised by the US Attorney's Office in the Central District of California. The head of that office, who serves at the pleasure of the President, is the US Attorney for that judicial District. It was he who decided to decline to prosecute, not a Member of Congress or the state's governor. Nor does he answer to anyone other than the Attorney General or the President.
Doesn't make his decision to shut the book defensible, but there is no evidence that he was compelled to do so by political pressures. (As an aside, it isn't hard to imagine a plausible motive unrelated to political pressures -- consider how well the recent prosecution of Clemens went for the government, the difficulty of selecting a jury, and the need to shoehorn a PED case to fit a mail/wire fraud conspiracy or RICO criminal theory.)
As to the other question -- information sharing -- it is possible that the FDA and the FBI provided their witness interview summaries to the USADA or information obtained from non-compulsory sources, although the FBI, at least, is rarely willing to provide that sort of information to non-law enforcement agencies like USADA. That said, the grand jury secrecy rule prevents them from sharing grand jury materials, either transcripts or subpoenaed records, to a body like the USADA there is no exception to the rule that would apply to arbitration proceedings such as this.
There is no doubt in my mind, however, that the FDA and FBI agents who participated in the DOJ investigation will monitor the arbitration, and if indeed a sworn statement is taken that directly contradicts a material aspect of the grand jury testimony of that same witness, I would not doubt that the agents will ask the US Attorney's Office to take a further look. But if the US Attorney lacked the will to bring the substantive case, then a derivative case based on perjury, obstruction, or false statements charges designed to vindicate the uncharged substantive case would be even less appealing to that US Attorney, I would imagine. Regardless, the witnesses will know what they said to the GJ, and consequently will be careful not to stray too far from that prior testimony.
Who knows. This is all total hypothetical nothing until the USADA produces its report and events begin to unfold.