Bradley,
I have not owned a Rainford's goby... at least, not yet!
I do have a Randall's shrimp goby in a 24 gallon Aquapod (Amblyeleotris randalli) with a green clown/coral goby. These two fish have no problems with one another, as they are in two totally different areas of the tank. Because my Randall's doesn't have a pistol shrimp to dig a burrow for it, it lives in a live rock cave towards the bottom of the tank.
I have read that the Rainford's goby is also a surface dweller. If your tank has sufficient rock work, I don't think the two together would be a problem. I have a firefish living w/ my gobies, and it also is a crevice dweller. The Randall's just opens it mouth very wide and flicks its dorsal fin when it feels the firefish (which is at least an inch larger than the Randall's) gets too close.
That being said, the Randall's is a relatively small shrimp goby, only growing to 3 1/2" and apparently growing to that size quite slowly. Since the Rainford gets to be about 2 1/2" I would suggest adding only a smaller shrimp goby (as some can grow up to 5" in length; your Rainford's would probably appreciate one no more than about 3 1/2")
You can look for gobies from the genra Amblyeleotris, Stonogobiops, Cryptocentrus, or Ctenogobiops. You may want to check if the species that you are interested in does infact pair w/ pistol shrimp. I would think that, as long you do not chose one that has horizontal stipes like the Rainford's, you will be unlikely to have problems with your current fish species.
Good luck! I hope you get to see your shrimp more often.