superb, this image made me want to watch The Lord Inquisitor even more - - - by the way, you should consider drawing The Grey Knights, maybe it would even serve for the glory of this "upcoming" fan movie as official poster/promo image.
It's actually a pretty nice place but it may occasionally be attacked. the tyranids, Iron warriors, orks, tau, and others would like a piece of Ultramar so I would say its still dangerous and grim but much less than most areas of the galaxy.
You know as for the Tau guys attacking I bet they would be in huge surprise when they see how imperials could be so nice to their own people.(Ultramarines being nice) And find it really hard to force them into the Tau Empire and make it look like a Kick the Dog