I read The Rogueries of Tom Moore thinking it was true, but today I see in an entry from Ulysses Annotated: Notes for James Joyce's Ulysses that it was a hoax. The entry:

Gifford:

8.414 (162:29). Tommy Moore's roguish finger – A statue of the Irish poet Thomas Moore (1779-1852) stands over a public urinal near Trinity College, opposite the east front of the Bank of Ireland. A fragile eroticism is characteristic of Moore's early verse. His most famous series, Irish Melodies (intermittently, 1807-1834), was to be found on the bookshelf of every properly sentimental Irish household. Moore left Ireland in 1798 and advanced himself in the drawing rooms of the influential in London. His laments for "poor old Ireland" were, therefore, not vital Irish rebellion but sentimental complaints acceptable to English ears. Moore's reputation was tarnished by his apparent willingness to compromise his artistic integrity and by the scandal that ensued when he abandoned his admiralty post in Bermuda and left an embarrassingly dishonest deputy in charge. His "roguish finger" is, however, an allusion to a famous literary hoax perpetrated by "Father Prout," pen name of the witty Irish priest Father Francis Mahony (1804-66), in an article, "Rogueries of Tom Moore," in Frazier's Magazine. Father Prout's hoax involved the charge that several of Moore's most popular songs were "literal and servile translations" of French and Latin "originals"; Father Prout duly "quoted" in evidence the "originals," complete with circumstantial historical background.


And if you're interested in reading The Rogueries of Tom Moore (quite a fun read), you can do so here (pages 211 to 261 in The Reliques of Father Prout) :

The Rogueries of Tom Moore