According to people in the know on www.boards.ie they will not work for Irish DTT.
They certainly won't work for HD, and RTE2 is already transmitting in HD, albeit they have a simultaneous SD transmission at the moment.
So best to get a set top box that is Saorview certified. AFAIK only a Walker STB from Powercity is currently certified but more expected to come available in the spring. Others may work (eg UK Freeview HD STBs)but may have problems with such things as digital text and interactive services.