I haven't used DADGAD tuning; but it seems to be a topic of conversation amongst fellow guitarists and it does produce nice results sometimes. It seems to me this tuning is a "D" chord (vestapol tuning) except that the third note is a semitone higher than it should be. Is it common in Celtic music to use this augmented third? After all, I can take vestapol tuning and press the first fret of the "F#" string to get that "G". The value must be in the fact that the "G" is open and rings. Is an augmented third common in drones?
(By the way, I just sung the first few words of "Don't fence me in" and note it uses the augmented third tone. I don't see the relevance of this either.)
Murray