A little known celtic era spanned western Europe, thought to have begun hundreds of years ago. There was possibly a two tier system in Ireland, though some gaels are believed to have joined the celts. The Cafferkeys were one clan that had a seat in Armagh; maybe became administrators for the celts, or in name only.
There has been little intermarriage. A reason being political differences. Celtic leaders reportedly departed Ireland following the saxon invasion. According to reports some returned. Often celts became administrators for the newly landed saxons in the same way as various gaelic clans during what was thought to be a Celtic empire, others were in opposition. The treatment of republicans, including family members has been the subject of much controversy. Sinn Fein, thought to be originally a republican party, and believed to consist mainly of celts and people of english descent are known for the ill treatment of Irish descent and often celts who resettle in Ireland as contrary to monarchic plans. Abroad the Sinn fein persona is staunch republican.
Ireland is believed to discriminate against gaels with regard to housing etc., but discrimination against the Irish, including celts abroad is worse, especially in the colonies where the monarchy receives the most support. A dispersal of the Irish is thought to be occurring, not totally understood due to the compliant who are thought to have been changing their names to Gaelic names for some time now. Businesses not thought to be owned by gaels still avail of Gaelic names, as do some politicians. All the above is believed to stem from monarchic plans for a British Ireland: Are the Irish government complying?