All Chase cards are good for Ireland as far as I know - includes MC and Visa, Biz and Personal, basic card to Signature/World/Infinite. Benefits are administrated by Card Benefit Services. Just give them a call, give them your card number, and they will e-mail you a personalized letter saying you are covered in both the Republic of Ireland and Northern Ireland. Takes less than five minutes. Some rental places may have requirements about the letter being dated XX days before the rental, so don't bother today if your trip is not for six months.
I also like to carry a copy of the benefits guide, just in case. If you don't have it - request a new one from Chase.