[dalke]

What you are saying is correct, but mostly in a pedantic sense. In the US context, "Dutch" name would mean "of Dutch origin", and not necessarily "as used by a Dutch person." (Many people consider themselves "Irish", despite being 3 or more generations removed from the Emerald Isle.)

The New York City neighborhood of "Harlem," for example, is a Dutch name even though in Dutch it's spelled Haarlem, and the original name for the place was Nieuw Haarlem. It's more precise to say that it's the English spelling of a Dutch name, but most people find that level of precision needlessly detailed.

I have no problems asserting that "Van Vlack" is an American spelling of a Dutch name.