I doubt if the term "session" was used in Ireland of any musical gathering (except perhaps jazz) until the 1950s; later, mostly, I'd guess; and pretty much contemporaneously with the use of the term in the UK for similar events. Everybody I know who grew up in areas where house dances and so on still took place (pretty much extinct by the '60s in most places, it seems; though of course there are exceptions) had never heard the term before moving to England. It's perfectly possible that traditional music was being laid on as a tourist attraction in some places earlier than that, but on the whole I doubt it; most foreign visitors (including Americans hunting for "Irish Roots") will probably have expected the "stage Irish" repertoire rather than the real thing; and it almost certainly wouldn't have been called a "session" at that time.