Originally Posted by The Glyphstone
As for the Rok's lack of warp capability, I don't think that was intended as part of the fight, that's just a general idea of the scale of force the Orks can bring to bear.
Would probably be a case of:
Space Hulk drops in, Orks leave the hulk, arrive in the Belt, build engines on asteroids- mine asteroids for metal to build tanks and whatnot- start moving inward- and Space Hulk drops back into the warp.
Alternatively they just break bits off their Hulk and head inward on those.