Benjamin Rigby wasn't sure whether he'd get to work with Fassbender. So it seems unlikely there are any other "David's" aboard the Covenant.
How can we be sure Ben Rigby is a) on the ship at all or b) not just killed before he has the opportunity to interact.
Its impossible to know whats happening.
Rigby could be a company man who appears on monitors for all we know, or some bizarre Engineer or God even!
As for the hat, it could be crew merch. Productions give that stuff out to crew and they wear the stuff on set. T shirts, jackets, hoodies,... Ive seen backpacks and all kinds of stuff.