I think that's true, Joan.
What I remember of my Scottish history includes that the West of Scotland and Northern Ireland were one kingdom, named Dalriada, with the same Gaelic language.
I don't think that Welsh these days is easily understood by Scots or Irish Gaelic speakers, but I remember hearing that it's closer to Manx, Cornish and Breton.
My in-laws are Irish Gaelic speakers but they're from Mayo in the West, and they reckon their Gaelic is distinct from even northern Irish Gaelic such as that spoken in Donegal or British Ulster. This strengthens the case for the Northern Irish and Western Scots Gaelic being similar, and distinct from the rest of Ireland.