It almost looks like you tried grouping by their last names alone, which isn't a great way to go. "Hoover", for instance, is the anglicized form of the German "Huber". Theodore Roosevelt, as Supersoulty hinted, was more Scottish than Dutch. The Bushes have significant German ancestry.
And the list goes on, and on, and on... several Presidents had Amerindian heritage, and Warren Harding might have been part African.
Actually, there's no verifiable evidence that any presidents have had Amerindian ancestry, despite rumors otherwise. Same thing with Harding and Africa.
Cite In Harding's case, I think the speculation started with Frances Russell's book
The Shadow of Blooming Grove. There's another book that was written a long time ago that speculated that five presidents, including Harding and Coolidge, had African ancestry, but again, genealogists find these claims highly unlikely.
Don't give Stark more fodder. Then again, I'm sure he's well aware of that theory.