"have you found any evidence"
Many of the older singers (not necessarily Travellers) certainly did work on technique - Joe Heaney talks about his awareness of technique on the interview he did with MacColl and Seeger in the 60s. I know singers like Paddy Tunney also worked on technique.
The revival singers are in a somewhat different position than source singers in that that many of them grew up surrounded by singers they could take their techniques from by emulation.
Also, and probably more importantly, source singers tended to confine themselves to a 'type' of song which they handled within a fairly narrow range of technique, while those of us on the outside were taking our repertoire from a much wider range of styles, requiring a larger grasp of skills.
As far as J. J. Niles's singing - personally it has never worked for me as I find it far too mannered and unsuited for narrative singing - but that's me.   
"Indeed you do Jim.............."
Oh dear - I'm being stalked by our resident dumber-downer.
Jim Carroll