According to a biography of McCormack, both of his parents were born in Scotland, so it seems unlikely that he was a native Irish speaker. Of course, if there were a lot of native speakers in the town where he lived as a child, he might have picked up some Irish from them. As to his accent, some aspects of this speech (especially the rolling R) reminds me of some Scottish people I have heard speaking in TV shows. I wish Scotcher were here to tell us if McCormac's accent sound Scottish to him.