[the scotsman]

Yes it is. That and Santa Claus. We know the St Nick name, but its not well used.

I gather Father Christmas isn’t well known or used in the US?.

[Verginius Rufus]

Probably most Americans are completely unfamiliar with the term "Father Christmas." The exceptions would be those who are aware of its use in Britain.

The poem "The Night Before Christmas" refers to St. Nicholas and St. Nick but never uses the term Santa Claus.