They're good to have, but there's no harm in having something prey on them. The small microfauna that'll live in there is good for keeping it free from uneaten food, etc, but the starfish will do that job too. One small SSSF wouldn't completely wipe out the microfauna, as they breed too fast, and run away from being eaten too! SSSF will eat the dead ones though. I could still see copepods buzzing around and amphipods scurrying around a year into having the SSSF.
I'd think they'd be ok, my massive orange spotted goby just minds his own business, but i haven't had those other fish in with it, although they're all supposed to be peaceful. The other goby might be cheesed off but it'll hardly be carnage...
EDIT: Live Aquaria says this about your Randall's goby, "It is not aggressive towards other shrimp gobies and may even share a burrow with another species."
A sifting goby will really get to work on the sand bed, though, they don't mess about... It'll look like a building site in there until it's built all it's burrows.