"As a nonacademic traditional singer from the sticks I very much doubt if Rae would even have heard of Child 40 years ago"

He may or may not have heard of Child, Guest gus, but the version he sings is pretty much word-for-word that published by Motherwell in 'Minstrelsy, Ancient and Modern' (read it here) in 1873. It's substantially the smae as Child's F text From Scott, with those rather poetic additonal verses about waesomely wailing snow-white sprites etc.

I think it's a mistake to assume that traditional singers from the rural working class were necessarily ignorant of published ballad collections. Mike Yates article about Joe Rae tells us that Joe learned songs from his mother and father, but also from his neighbour, the shepherd Ned Robertson, of whom Yates says:

"many of Ned's texts are similar to those published in the late 18th and early 19th centuries by the likes of Herd and Motherwell... Joe's ballads reveal a literary influence from perhaps a couple of hundred years ago."

He also quotes Alan Lomax thus:

"The Scots have the liveliest folk tradition of the British Isles, but paradoxically, it is the most bookish. Everywhere in Scotland I collected songs of written or bookish origin from country singers, and, on the other hand, I constantly encountered bookish Scotsmen who had good traditional versions of the finest folk songs. For this reason I have published songs which show every degree and kind of literary influence."

And I hate to rain on too many parades at once, but John Minear's transcription (and thank for all those, John) from Edith Price of Newport, RI, looks an awful lot like a collation from the two versions of the ballad in Motherwell's 'Minstrelsey'. If the singer did indeed give it the title 'Daemon Lover', that alone would be grounds for suspicion.