Yeah, catching them is the hardest part. Hopefully you won't have to though!
I really don't know about the dottyback - if it has so far been friendly with your other fish (poor shrimp though), I would think it would be ok to try? True they have a similar body shape, but the fang blennies are more open water swimmers than most dottybacks, so hopefully the blenny wouldn't be viewed as encroaching on the dotty's territory)...
I really wanted an orchid dottyback for that bright flash of purple but... so glad I didn't get one - considering I have a lot of inverts, some even trained to eat out of my hand (skunk cleaner shrimp and fire shrimp). Still a beautiful, cool fish though.
I think you'd enjoy a watchman goby - so much fun to see them interact with a pistol shrimp. Very peaceful. Some get larger than others (I want to say, of the watchmen, the yellow gets up to 4" - others will max out under that).
You can google which watchman gobies pair best with which pistol shrimp. My LFS often has YWG in stock already paired with tiger pistol shrimp. I think I would worry a little about your dotty trying to get at the pistol shrimp... but not sure. The goby would try to protect the shrimp, but can't really do more than open their mouth real wide and try to intimidate other fish. Not sure it's worth potential scuffles between the dotty and goby.