This is an area which neds careful investigation. There are many wild claims. My use and knowledge of the Sam Henry Collection (not just the published part edited by Gale Huntington and Lani Herrmann but his unpublished collection and that made at about the same time by other people working in the same area of north Antrim/north Londonderry) makes several things certain. Both broad politico/religious traditions sang; they sang mostly the same songs which showed signs of Irish, English, Scottish and some European influence - some even came from North America having originated there; both groups had some songs which were not usually sung, except in situations where there were none of the other group present, which supported there own political and religious position.
These statements are supported by a collection of more than a thousand songs which, because they were presented in a newspaper and because the songs or information about their singers was sent in by readers, is certain to have been more or less representative. More or less, because a newspaper (in the period 1923 - 1939) could not have published bawdy songs or any but the mildest political songs.
Today unfortunately, "Ulster-Scots" have allowed themselves to believe that their culture is represented musically only by the extreme sectarian end of what their section of north Irish society sang sixty years ago. Similarly the "Ulster-Irish" presently tend to deny that much of what they perform as mainstream Irish music and song derives from England and Scotland.
It is time, in my view, that Ulster-Scots reclaimed the mainstream of their musical heritage and time the Ulster-Irish admitted the part played by Ulster-Scots in theirs.
Incidentally, the Scottish Pipe Band Association in Northern Ireland is supported by bands whose membership is drawn from Scots and Irish Ulstermen and women.