The Back Room Boys are the brainiacs. The smarty-pants. The techies. They're the scientists and engineers behind the new technologies that Grandpa gets to take to the front. The Back Room Boys are pretty much detached from the practical applications of their inventions, and though scientists aren't all like that—especially these days—Dr. Seuss might be trying to make a point.
These cheerleaders represent the revelry that often accompanies nationalist pride. What fun! When Grandpa returns after the Kick-a-Poo Kid fails to be better than the Zooks' Eight-Nozzled, Elephant-Toted Boom-Blitz (say that ten times fast), they cheer, "Oh, be faithful! / Believe in thy butter!" (122-23).
By making nationalism a matter of faith, these guys seem to make the situation worse. Why? Because faith doesn't require proof. That means that the Yooks can believe they're superior without having to demonstrate it.