Denis O'Hampsey - his songs
It seems likely that O'Hampsey sung in Irish though it is hard to tell; it does not seem that any of Bunting's Irish speaking secretaries visited him to collect song words. In Bunting's pocket notebook he has scrbbled an English translation of the words to Burns March which can be sung to variants of the tune.
Many of the pieces that O'Hampsey played were Irish song airs. Some were completely straight e.g. Aisling an Oigfhear (The Young Man's Dream) while others are arranged to a degree that makes them pretty much unsingable e.g. Éibhlín A Rún.