Condemned takes place aboard a human frigate, Unearthed has open spaces and Highland is a giant Covenant cruiser blasting a planet.
It's French sitethat claims to have the leaked screenshots. Their website was temporarily down as Microsoft requested they remove materials relating to the Defiant Map Pack. That sounds like solid unofficial confirmation right there.
Theirstill has the leaked map pack shots.
Rumour: Leak reveals Halo: Reach 'Defiant Map Pack', 3 maps
10 February 2011 | By Simon Priest