What a find!
Yes, some of it was used for "An American Band", possibly also for EH.
One of the songs they perform in their yellow shirts seems to be "Monster Mash". Don't know about the others. One features Carl on the lead spot.
A new Beach Boys documentary would certainly be well advised to look further into material like this imo. Especially since we don't have any other footage of David and Al in the band during this time if I'm not mistaken. I guess the original footage is in David's personal collection?
EDIT:
You also see the band backing two female singers. According to David, “we played back up musicians for Dee Dee Sharp and Jackie De Shannon. The Treniers were kind of a Vegas act and we became good friends with them as well. They were great guys.” (Quoted by Ian on his
Beach Boys Gigs entry Friday June 14 to Sunday June 16, 1963)