While the original source of the myth/legend/story about the consequences of angels "literally" coupling with mortals is unknown to me, it does seem to be a theme rooted in Irish folklore. The metaphoric applications are infinite, as in this song, Raglan Road, where the final reference to the plight of a clay wooing angel elevates the singer's sorrow to an ethereal plane. I don't hear in it the singer referring to himself as an angel/artist. That would ruin it for me too if I heard it that way. To me, the angel reference is a bit of irony the singer takes for solace. I've only heard the Van Morrison/Chieftains version, but it made quite an impression. An interesting cinematic illustration of this theme is the movie "Gotham" w/ Tommy Lee Jones and Virginia Madsen.