David,

There would undoubtedly have been many cultural contacts such as you suggest but all would have taken place long (seven or eight hundred years) before the coming of the kilt. We must not get into Hollywood anachronisms like "Braveheart"!
On the specific question of Dal Riata, recent archaeological findings by Ewan Campbell of Glasgow University suggest that the previous belief that any q-Celtic artefacts found in Scotland must have come from Ireland may well be false.

http://www.electricscotland.com/hist...scotsirish.htm

There must have been periods of close liaison across the water but equally periods of dispute. Peace treaties did not last long in those days!
Certainly current linguistic thinking is that p- and q-Celtic diverged far back in Gaul and that there were q-Celtic speaking tribes on the mainland of Britain as well as in Ireland - i.e. they did not exclusively emigrate from Ireland. Whether the Irish and Scottish tribes would have had any commonality other than language is not clear.

Alan