I'm told that the IAA used to accept UK CAA JAA ATPL passes for Irish JAA license issue but have now changed their mind and take the view that, if you want a CPL issued in Ireland, you have to do all your training there. This is second hand info, so it would bear checking.
The IR, on the other hand, is not required for CPL license issue. As an additional rating it can be flown under any JAA state's jurisdiction. You should be able to do an IR in Ireland and tag it on to a UK issued CPL.