As for the "Wild Geese" in "The Foggy Dew" it is pretty clear that Father O'Neill when he wrote it was indeed referring to the Irish who had joined up to fight the Germans.

Otherwise what could these lines have meant?

It was England bade our Wild Geese go,
That small nations might be free.
But their lonely graves are by Suvla's waves
On the fringe of the great North Sea
............
My own father saw no contradiction between fighting for the Irish Republic in the Civil War and fighting in the British Army in World War II. When in a civil court case one time many years later a magistrate expressed surprise at an IRA veteran having being willing to put on a British uniform, he said "I always
was one to stand up for the rights of small nations. Even my own." And I'd be pretty sure he had that song in his mind when he said that.