The Imperium will tolerate some aliens who serve a purpose and are willing to be branded and are vouched for by a powerful patron such as a rogue trader or inquisitor. There was one official model released of such a sanctioned alien – Krashrak the Stalker. And an alien booster pack was also released with alternate heads and additional weapons.

Fortunately quite a number of alien creatures have been produced by other companies at 54mm.

Alien Sniper (by Wildhouse models, left) and Krashrak the Stalker (right)
Sanctioned Aliens (Newark from Smartmax) (left) and another Krashrak the stalker (right)
Alien bounty hunters. The alien (left) was purchased. It’s a great conversion using a clawed fiend. With the alien on the right, I’m not sure of the manufacturer. It is made of a soft plastic.

I have another few aliens that i will eventually paint up.