The IRA conducted many attacks against the British totally regardless of the war with Germany, but they also actively worked with the Germans against the British.
|IRA Soldiers in traditional getup|
Another series of IRA attacks was The Northern Campaign. This started roughly three years after the outbreak of war. It lasted about two years and was largely insignificant. The IRA lost 3 men during the campaign, whereas the British lost 4 men, plus loads of supplies and infrastructure. The campaign more or less fizzled out in 1944.
The Germans picked up in the IRA-British conflict and exploited it, mainly for intelligence. The intel gathered by the Germans was fairly trivial, but not totally insignificant.
All in all, the IRA made very little difference to the war, but it wasn't for lack of trying.