off the top of my head tim the cloaca in males is used for pheremones in the way you are asking. they have villi in there and the extension of the surface area helps to expose their pheremones to the aquatic environment more- it is my impression that the bigger more exposed the cloaca the 'louder' the advertisement of scent. i think it is in the book you mention that they have done research on JFB's to show that the groves down the body in males help areodynamically in their ability to waft scents foreward with their tails. so when males are most excited they extend the cloaca as much as they can-you can watch this in pachytritons when they get excited by a new member in the tank or when a female is taking interest in them, their excitement shows itself by the eagerness in which they fan more and the cloaca swells, some even are seen to be straining almost in the effort. my understanding also in the seasonal bulge in the males vent is the activation of the glands which produce the mucous for spermataphores. the sperm is created in the testes but the mucous is created in situ in the cloaca.
btw i will post the pic of my females crest to show what i mean in a separate post