My knowledge of the period is sketchy, but the identification fits with the historic origins of the Scotti and the Dal Riadan community which took over the kingship of large parts of modern Scotland from the Picts, the reference to Gaelic as 'Earse' - 'Irish' etc.

Unsurprisingly both the main interpretations of Celtic languages place Scots Gaelic and Irish Gaelic closely together (with Manx) compared to Old Welsh, Cornish and the limited impressions we have of Brythonic and Pictish.

The connection of Highland culture to Irish culture seems to have gone beyond the simple result of proximity, but I know nothing of how highlanders of this time saw themselves, or how this affected their view of the Norman nobility.

Of some recent interest to me at the moment is that the current limits of genetic testing of male lines can distinguish a strain of 'Celtic' from typically Germanic or Scandinavian, but that this is common to (in descending order) the West Coast of Ireland (up to around 90%), East Coast, Western Wales, Eastern Wales, Scotland and even England (still around 60%) - basically reducing as you get nearer to London - showing not only that Scots and Irish families share a common ancestry, but so do the Welsh even the majority of people born in England, who apparently aren't as 'Anglo-Saxon' as they probably seemed to historians from the Norman period on.