I don't think there are any hints about what was in those tombs. But as always: you can put whatever you want in those caverns.
Ancient automated defence systems or traps are absolutly ok. Things like that make an adventure more exciting. Lets say: they are the scifi version of our good old fantasy dungeons, where danger lurks behind each corner :-)
Concerning the Tyrant Star: My advise is - don't aim too high. Of course you can build up your story around sector shaking things like the Tyrant Star if you and your players like it. But they make a story very complex. And complexity is not always easy to handle in a roleplaying round.
Personally I don't like my akolytes solving all those ancient secrets of the sector. They are after all just very small henchmen of a sector spanning institution. So I let them find scraps of information about hideous secrets but more for the benefit of the dark and horror feeling of Warhammer 40k. The Tyrant Star stays an unexplicable horror.
But that's only my personal favorite approach to Dark Heresy. You must find your own