Arthur Ó Néill (c.1737 - 1816)
I have not been able to track down very much information about Arthur Ó Néill singing. Our main sources of information are silent about this; Bunting in his music collecting concentrated on instrumental versions of tunes, and his notations from Arthur Ó Néill are all indicated to be harp versions. And in the Memoirs, Arthur Ó Néill does not mention himself singing very much. He often mentions other harpers singing, and he mentions himself playing the harp.
I presume that Arthur Ó Néill sung a fair bit, as singing was a normal part of early Irish harp performance practice in the 18th century. I presume that he knew the words to all of the songs whose tunes he played on the harp.