They’ll do fine together, I have a pink bar goby (which is watchman) and the Tailspot in a 28g. Watchman gobies are pretty cryptic and usually sit at the entrance to their hole, or mine sometimes perches on this colony of zoas just above the rock her cave is under. Whereas the blenny is constantly going from hole to hole (it has probably 10 different little holes/crevices it maintains all across the tank), eating algae off the rocks/glass in between. The blenny has a main home where it sleeps (underneath a Hollywood stunner that’s plating out), but it keeps a bunch of other hideouts clean (she keeps them clean of detritus/algae/hermit crabs, she’ll grab whatever it is that she doesn’t want in her hole and carry it to the other side of the tank and drop it). One of my favorite fish, is active and has tons of personality.