marinefish-
I was going on my own experiences and stories I have heard about the pistols being somewhat aggressive, but after doing some research on them, seems I may have been a bit harsh in my last post. My humble apologies if I freaked you out... They certainly are not in the same category as mantis shrimp. Those little buggers are really nasty.
You are correct about them having symbiotic relationships with certain fish, and actually anemones as well. (made me want to get one) :-} The thing I did remembered in regards to them being reef safe, is that because of their tendency to dig in the sandy substrate, they can undermine reef structures that are not secure. Meaning small pieces of LR that may topple and crack a tank wall. That seems easy to prevent though, so not much to worry about really.
As far as aggressiveness goes, seems to be somewhat dependent on the individual. I had a coral banded shrimp that attacked my hermit crabs, dragged them out of their shells and ate them. Also ate an unluck turbo who got caught upside down. Coral banded shrimp are not usually thought of as that aggressive except toward each other.
My solution to stopping my shrimps destructive behavior was to keep her fat and happy. She loved cocktail shrimp. Used to literally fly up the side of the tank using her back swimmer feet and take it right from my fingers. Sadly, she was eventually killed by my Basslet. Caught her unaware I guess.
Sounds like your goby should do OK if they are bonded. I'd still watch out for any aggressive behavior, especially towards your cleaner shrimps. But like I said, make sure he/she has enough to eat, and you should be fine. :-} angus