You can't deny Moscow's admition is proof there was positive work during the Bush administration.
There was some very positive work done with Iranian collection under Bush but Moscow's "admission" has nothing to do with proof and everything to do with plausible deniability for Russia to oppose action against Iran in the U.N.
By playing dumb for a bit Moscow gets to say that they have no corroborating proof of Iranian nucler ambitions and neatly block U.S. moves diplomatically. A neat move but it has nothing to do with the actual state of the Russian intelligence service's collection on Iran.
Russia puts people openly on the ground in Iran by the thousands (they are a massive business partner of Iran). They don't need to scre around peering over borders electronically, trying to infer data from thridhand sources, or paying dubious insiders for juicy but false HUMINT. All the Russians need to do is look around to see what is going on in Iran as ground truth.
Taking Russia "admission" at face value is laughable and has nothing to do with President Bush's relatively solid management of intelligence collection (there is still so much room for improvement... you woulnd't beleive how bad it got for a long time).