My guess is Cheney knows that can't happen because they have secret info so he feels safe to bluff.
If there was hard evidence that torture prevented an attack at it could be released the Bush administations press department (AKA Fox News) would have plastered it all over to support the administrative's position.
I could be wrong. But given Cheneys past record for veracity, I feel pretty safe putting this in the "skeptical" department till shown otherwise.
There is a very strong chance that your guess would be wrong. They just need to declassify all the documents, and not cherry pick them to bolster their agenda. Seems fair if they declassified them all.
As long as they don't compromise any intel agents or anything, I don't have a problem with that.