Just doing some research for a short story. My intial google searches have informed me about Operation Green and 'The Passing of the Great Race'. The Irish have been on the receiving end of a lot of racism all across the world. Were the Nazis any different? Would they have been treated like Slavs and Poles?
Ireland referred to World War 2 as "The Emergency"; you'd find British pilots were generally better treated than Nazi ones if they came on Irish soil. Quite a few Irish joined the RAF, and firefighters were sent across the border to help put fires out in Belfast when it was blitzed.
"In the past, and probably in the present, too, a number of them did not see eye to eye with us politically, but they are our people – we are one and the same people – and their sorrows in the present instance are also our sorrows; and I want to say to them that any help we can give to them in the present time we will give to them whole-heartedly, believing that were the circumstances reversed they would also give us their help whole-heartedly" - Irish taoiseach Eamon De Valera, Castlebar, 20 April 1941.
The Nazi's seemed to see the IRA as a thorn in the British side, and tried to use them. Early in the war, there was some sympathy from Ireland; the Germans had provided guns used in the Easter Rising during WW1, but public opinion swayed within a year or so. There wasn't exactly strong love for the British either of course, what with the war of Independence being just 20 years earlier and events like Bloody Sunday at Croke Park, but needs must. The fact the Luftwaffe bombed Dublin in May 1941 didn't help...