Has it been revealed what Jugo and Sugeitsu found in the lair?
Yes, it was revealed in the manga. The scroll is a Jutsu Scroll for Shiki Fuujin: Kai, the method to unseal the Dead Reaper Seal.

It was thanks to this that Orochimaru was able to revive the 4 previous Kages, whose souls were originally sealed within the Death God.