The original poster spoke of "kilt wearing Americans". That seems to be a very broad church and most Scots are probably very happy with some members but less so with others - it must depend in entirely on motivation. For example, the vast majority of Scots see Utilikilts and the like as just a big joke and certainly nothing to do with Scotland. I guess that we could have some concerns about sites like this one and various US "gurus" causing misinformation and myths to be endlessly passed around until they become the truth. You only have to look at the locations of Xmarks members to see that there is very little Scottish representation To put the question the other way round, what do Americans think of Scots singing C&W songs. C&W clubs are very popular in Scotland especially here in the North East. If some farmer from Auchnagatt or a fisherman from Buckie who has never been near the States composes a song about his forty-tonner thundering across the prairie (or whatever), can that be regarded as in any way authentic C&W?
To recap, Scots are very happy for the tartan to be worn by Americans for many possible good reasons provided the tail does not come to wag the dog. The kilt is Scotland's National Dress!