I question your opening statement. Do we actually know if the "Irish style ornamentation" existed prior to union pipes, or, if it did exist, if it was even the same as what we think of now? And, are you sure you have it the right way around - ie, was it pre-existing irish style that influenced players of union pipes or was it players of union pipes who influenced irish style ornamentation?
That is an interesting way of looking at it. Pipe ornamentation has definitely influenced the way other Irish musician's ornament their playing, but the reverse must also have been true too! There was a strong musical tradition that predated the arrival/development of uilleann pipes in Ireland. There's no doubt UP pipers added to the way the music was played and ornamented, but personally I can't believe one instrument could change the way a whole tradition sounds.
Although close relatives, and sometimes musically incestuous, Irish, Scottish, English and Welsh folk traditions do have a different accents, and to my ear the accent comes from the ornamentation (and I guess phrasing too).
John - Everyone of the pipers you mention are Irish pipers, playing in the Irish tradition. I'm trying to understand if the Uilleann pipes would have sounded different in an English or Scottish setting.
EDIT Wow I sound so snarky there John, sorry. I was rush posting from work