i have heard of a celtic faire being used as a front for hate-mongers. and the participants were not even aware that they had been used this way until the event was over!
Doesn't sound like it particularly successful.
All "races" in the world are quite mixed up in the concept of being "racially pure." The only communities that aren't are those that are on the extreme fringes of the world - such as the Sami (I think that's right - the Lapps) in Finland/Sweden/Norway.
The Irish, Scots and Welsh are identifiable as Celtic, but aren't all that "racialy pure." It is likely that the typical Irish person has Celtic, Germanic, Norse and possibly even Latin DNA.