I was not aware of the statistics you cite, but Scorsese's "The Gangs of New York", set in Five Points immediately before the Draft Riots, has a scene in which Irish immigrants are enlisted as they come down the gangplank.

On the other side, Patrick Cleburne was an Irish Protestant, born and raised in County Cork, who came to the US in about 1850 and wound up in Helena, Arkansas. He had served for several years in the British Army. When the war came, he helped to organize and trained local volunteers, who were ultimately absorbed into the Army of Tennessee. He became probably the best Confederate general in the West, seeing heavy service at Shiloh, performing extremely well at Stones River, and saving the army at and after Chattanooga. In the winter of 1864, he proposed to Joseph Johnston and other senior commanders that the Confederacy incorporate Blacks into the army; needless to say, the proposal was turned down (the Confederacy ultimately began doing so in the closing months of the war). He was, in effect, murdered by John Bell Hood at the Battle of Franklin on November 30, 1864 when Hood destroyed his army in a fit of anger and revenge by sending it against entrenched Federal positions.

• Stonewall of the West