Interesting list of suggestions :-)
Okay, it's an old post but the main subject can still interest someone looking for Irish music for a mass.
The choir I was in a couple of years ago did an interesting Irish Mass piece, with the original Irish Gaelic text. It might be difficult to set up for a wedding though, since it includes a string orchestra and pipes, whistles and harp :-)
This piece has been written by an rather unknown french composer, Gilles Mathieu. Although I have som doubts on the accuracy of Irish word settings, it does sound really good especially because of the presence of Irish instruments.
In any case there are more info on the composer's website

hope this helps someone, someday...