There is something I'm curious about: how much information are you given when you are making art for the FFG 40k RPGs?
The Dreadnought armour of Brother Szobczak is a standard pattern rather than the specialized Ironclad siege breaker and the Tau appear to really be freaking out over the Ghanataar* when they are allies in the book.
Did they leave this information out when this piece was commissioned? Was the book not fully written at this point and the details of the adventure had not yet been hammered out?
*Not an Enslaver, but they are a Warp-corrupted Xenos race with psychic powers, so there's some overlap.