You bet we will!
I have no epithets for you, Sandman (well, maybe "chauvinist" suggests itself), but there is no earthly - or Discworldly - logical reason an American could not portray Sam Vimes brilliantly. Many British actors have portrayed Americans without American audiences crying foul. Daniel Day-Lewis (OK, I know he's Irish) played Abraham Lincoln, for crying out loud! My own first choice to play Vimes has portrayed Englishmen at least twice before.
. (Holmes and Chaplin) As an aside here--Renee Zellweger played Bridgit Jones so well that fellow actors who did not know her before refused to believe she was a Texan. And speaking of Texans - going further aside - have you seen Michael Caine in Secondhand Lions? He portrayed a "good ole boy" Texan flawlessly. And I am one Texan who can spot a phony drawl a mile off!
All in good fun, of course, Sandman.