Hack is just a word, Dick. It doesn't necessarily have negative connotations. The word in this usage just says that he was operating at the very bottom end of the market and trying to eke out a living. What they produced is like everything else produced for a commercial market, a whole pile of shite with the occasional jewel, as Child inferred. Time sorts out the former from the latter.

It's an excellent song and we have both sung it I'm sure. I think it was originally intended for the 'Rose Tree' tune but I always used the pretty Irish tune.