All of the rail passes I have purchased have had my passport number on them. It is written in by the agency selling the pass. Conductors may request to see your passport to verify that you are the person entitled to the rail pass. Showing an Irish passport would probably result in having your rail pass confiscated.
See more about riding the rails in Europe on my page at
http://www.enjoy-europe.com/hte/chap17/rail.htm
John Bermont