Whether Roddy's name is Gaelic is not necessarily to say he was Catholic. Don't forget many Ulstr Protestants wer of Scottish stock. Wolfe Tone was Protestant, as was Henry Joy McCracken (I believe).
Shane McGowan's version of the song is a joke. For someone who knows so much about Irish history and culture (as he claims)moved McCorley's death from County Antrim to County Galway "on the bridge of Tuam today".