Hey, I have that book! It is a great book; I highly suggest it. Although I refer to my Borneman and Scott Michael books a bit more frequently, it is a close third.
The book doesn't mention any Ecsenius spp. specifically. As far as sexual dimorphism, it can often be determined by the fish's genital papilla (you may need a magnifiying glass to really get a good look.) Apparently, a male's genital papilla is long and tapered while the female's is short and blunt (and this is easier to discern if you have the two to compare.) I only skimmed the blenny chapter; it seems as though blenny gender allocation is not yet known but at least the genus Meiacanthus (the fang blennies) are believed to be gonochorists (born w/ a predetermined sex.) Despite this, the book states that "outside the spawning season" males tolerate the presence of other males.
I have read over the chapter on gobies multiple times. For most sex can be determined by using a hand lens to examine the genital papilla (female's is short and blunt, "roughly equal in length and width" while the male's is elongated and tapered.)
Given that the family is so large, the gender allocation types are all over the board, even within the same genus. Apparently, the various neon gobies (Elacatinus spp.) are gonochorists, yet the greenbanded goby (Elacatinus multifasciatus) is a protogynous (female to male) hemaphrodites. The information on Gobiodon spp. is based on G. histrio (as it is the most commonly studied), but it is believed to be valid for all the "coral" gobies. They have been found to be protogynous with the protential for bi-directional sex change. Apparently, they are naturally found in social units much like a clown fish, although they are controlled by a dominant male (instead of a female) and their coral head is their anemone. Only the dominant female is functional and spawns, and she moves up the chain of command if something happens to the male. According to the book, if two males are isolated on a coral head, the submissive one reverts to its female sexual function.
Interesting stuff; the book is a good read.
