Only if it helps me win. 

I'm not sure that it counts as a mistake. The extra officer is manning the roadblock as Rosco drives off, and then he moves the barrier when he come back through. The Hazzard County Police Department was much larger in 'One Armed Bandits', and Boss hired many deputies throughout the series, it's just that this one isn't referenced in the storyline. 

That yellow truck in Arrest Jesse Duke, is the same one from The Ghost of General Lee?

I caught one in Season 2 Dukes Meet Cale Yarborough. When Rosco leaves the road block, and turns around comes back the other way. There's only him and Enos. They're the only Hazzard County cops. But an officer in a Hazzard County Police Department uniform moves the yellow road block barricade out of Rosco's way. Who is this mysterious Hazzard County Officer?

Season 2 The Ghost of General Lee Phil:"Ernie, they're comin' after us." Ernie:"Cops?" Phil:"No. The whole blame town."