Other than Forward Unto Dawn are there any novels or anything that covers what 'ol master chief was up to during the gap in the book. I believe it is 2525-2552.
Very little to none. Interestingly enough one of the most unexplored aspects of the Halo Universe is the Human-Covenant war. More specifically the 2530’s-2540’s. All we know about what Chief was up to was, FUD in 2526 his brief appearance in the Babysitter in 2531 (Halo Legends), Rescuing “the package” in 2544, then sigma octanus in 2552. That’s about it.
In Ghosts of Onyx, there’s ONE chapter where its Chief point of view during a raid on an Insurrectionist base in 2531.
Dang, I want more stories from Blue Team in this time period. It feels so… void. 
He and Blue Team also fought in the Battle of Jericho VII in 2535.
Maybe they will go into it after Halo 5 when we actually get to control Blue Team.