Here I am answering me own question... rummaged about for my well-thumbed copy of Frank Harte's Songs of Dublin where he says this about 'Red Roses for Me':

"Like many of the songs that O'Casey wrote for his plays, he set them to well-known airs. This one is sung to the air of 'Eamonn an Chnuic' or 'Ned of the Hills'"

so there I have it.

I was amazed to find, while looking for the original thread, another thread mentioning O'Casey where Frank Harte himself surfaced as a guest contributor. Makes the world small, this Mudcat..