I don't know about Australian music, but definitely the music that was imported to America has developed into a completely different animal. American folk music has some of the same sound as the older Celtic/English/whatever folk that it evolved from, and there are American versions of a lot of war songs ("Johnny I Hardly Knew Ye" is a good example of this). Also, a lot of American labour songs were adapted from earlier folk music. Modern Country and Bluegrass music both have deep roots in Celtic music. All modern folk rock (Jethro Tull, etc.) have a huge amount of Celtic sound. Etc.

Really, almost all music has some sort of tie to Celtic music (at least in America). Of course the extent of those roots varies greatly between genre and artist. . .

Peace--Keli