Stan Hugill in his book Sailortown (1967) has a chapter "Fiddler's Green: a composite sailortown". He doesn't go into where the term comes from or how it got attached to the boozer and brothel and boarding-house area near the dicks around the world, he just uses it as a term to refer to it.

One such of course being the Holy Ground in Queenstown (Cork).

Stan's book is a sort of retrospective gazeteer of Sailortowns all round the world. Fleshes out what all the songs are about. Invaluable - and therefore naturally, out of print.