This can be categorized under FWIW - Google Books has a facsimile copy of the Cox book online, complete with the four American versions of the gypsy song that he had heard or collected himself, going back as early as 1880 - which is the oldest date I have found so far with a gypsy-themed song that includes a chorus of nonsense syllables like the Scarborough/Maguire "ah dee doo."

Cox's Gypsy Songs

Child#200 and its variants have no chorus beyond the repetition of the "gypsy-o" or "Davy-o" phrase at the end of each verse.

Further - the University of Wisconsin Digital Collections has a .pdf of the musical setting for a version of "Gypsy Davy" collected in that state in 1946 and featuring, like the Scarborough version, a tune in a major key with a nonsense-syllable chorus.

Frances Perry's 1946 "Gypsy Davy"

I may be able to make a MIDI of this and if so will post it, but it is similar to the "Gypsy Davy (Widdermer Schauffler version)" already posted in Mudcat MIDIs here. Both the Perry and Schauffler tunes are very close to Maguire's, though not identical.

What this says is that Maguire composed a little and cut and pasted quite a bit, however he may have heard the tune and picked up all the American tropes like crossing the plain/hills, singing sweetly, going down into the valley, and so on. Maguire may - MAY - have changed "lord" to "father" and made the gypsy a lord (though once again there seem to be wraggle taggle variants that include these), but in any event, like it or not and abomination or not (as above), "The Whistling Gypsy Rover" has a legitimate pedigree as a folk song that, while a variant of "The Wraggle Taggle Gypsies" is not a Tin-Pan-Alley type composition cut from whole cloth by Leo Maguire.