How long did they stay in Northern Ireland? One would assume there would have been some Scots-Irish marriages somewhere in there, if they were there for any length of time.
Remember that the term "Scots-Irish" does not refer to a hybrid of Scots and Irish, but to Scots, both Lowlanders and some Highlanders, who resided in Northern Ireland as part of the Ulster Plantation. In general (and there are always exceptions), the Scots in Ulster were Protestant and did not marry their "native" Irish neighbors, who were Roman Catholics.

Cheers,

Todd