Conversion is fairly basic, but the Dwellers are essentially supposed to be a gross humanoid alien that represent the survivors of a crippled alien race that tried to tangle with the Imperium a few thousand years back, The Dwellers were created in the FFG Rouge Trader expansion 'Kronus Beastiary' which has a whole series of charts for random generation of alien flora, fauna, and civilizations. We came to the conclusion of semi-slug semi-bird like creature, with this disgusting style of out-of-body digestion being a commonality among the natives of their homeworld.
The tyranid arms are there to represent your basics of an alien crafted bio-weapon, pistol, shotgun and rifle, all of which will likely be fairly apparent given the design of the weapons.
These are the Tau from the last AAR, their newly added Dweller or My'calo in the language of the Tau.
As for the Rouge Traders from the previous AAR, they can be found here!
The "Shore" Party - Link