I found something about this in MacLysaght's 1980 The Surnames of Ireland. In the introduction it says:
"The Cromwellian Settlement was different [from the plantations in Ulster ] because the immigrants introduced were widely scattered over the country. In this case they were for the most part eventually assimilated and became an integral part of the Irish nation. Generations of intermarriage with native Catholic Irish have made them, apart from a few landlord families, otherwise indistinguishable from their neighbours who bear Gaelic or Hiberno-Norman names."
--- In firstname.lastname@example.org, "mhbowes11" <martha.bowes@...> wrote:
>My family, with Scandinavian haplotype, appears in the Catholic registers in the late 1700s >and was thoroughly and self-identified Irish. I have not seen anything as to whether many >of the loyalists who came as part of the S&P converted to Christianity and became >thoroughly Irish or not. I'm interested in anything anyone may have on this, because there >is an apparent contradiction (or is there?) between the Scandinavian haplotype and Irish >Catholic religion in the same family if they came to Ireland with loyalists.