It's a genuine tradition.  "Ulster Scots" were originally 17th. century Scottish immigrants to Ulster, who were encouraged to settle there as part of the strategy intended to end resistance to rule from Westminster.  Memories being long, the term is still used of Ulster Protestants, though many of the families have been there for hundreds of years, now.  There was also a great deal of immigration from Ulster to America from before the time of the War of Independence; a lot of people in America and Canada, for example, trace their ancestry to Ulster Scots.  Quite apart from the Plantations, there has always been a lot of commerce, both economic and cultural, between Scotland and the North of Ireland, which of course are physically very close; migrant workers, for example, going over for the potato and fruit harvests.  As might be expected, songs, tunes and dances have also made the journey in both directions.  A lot of songs of Scottish origin are to be found in Ulster, and dance-forms like the Highland and German are particularly popular there.  The band Altan, to name a well-known example, play a lot of this material.  Equally, a lot of material of Irish origin has found its way into Scottish tradition; such exchanges always work both ways.

Malcolm