Deputy Otis - S2-E31
Visible crew/equipment: After Otis admits to Andy the reason why his brother thinks that he works at the courthouse Otis walks back to the cell, but when Andy calls him back and gets up, just as Andy walks around the desk we can briefly see two actor's marks where they will stand momentarily.
Answer: It was a joke. They were supposed to be dumb hillbillies.
Both. According to later interviews with both Andy and the Dillards band (the real name of the band that played the parts of the Darling children, of which Charlene (Maggie Peterson - Mancuso was also a member) the reason the Darling boys never had any lines was because they would've had to have been paid if they spoke. In return for appearing without lines or pay, Andy promised to get as much of their music onto the show as possible which, he did. This obviously gave them a lot of exposure.