So, the Google DNS servers are returning the correct values? Is it definitely Google's server which has been hacked?
It looks like either the IEDR (the guys who manage .ie) have been hacked, or, either Google or eMarkmonitor Inc (whoever they are) had their password for the IEDR systems compromised.
I was about to say that points the finger at the IEDR, but.. "eMarkmonitor Inc" are involved with them too..
# whois yahoo.ie
...
person: eMarkmonitor Inc
...
That basically means eMarkmonitor or the IEDR were hacked/had passwords stolen.