Chuck,
Great job on the interview.
Nobody's asking the guys in the field. The border patrol previously had M-16 A1'sand M 14's, however I don't think they are authorized anymore. For example, my agencies firearms policy allows pretty much any government issued M-16 or a are 15 variant but when we asked about DRMO rifles we were told that our issued/authorized weapon is the colt M4 carbine, not the M-16 A1. I would much rather have an M-16 A1 with an aim point in a gooseneck mount then no rifle at all but in a nationwide agency with 20 or 30,000 officers streamlining logistics and training does make a difference from the agency perspective.
Re: the union dude, I don't think US customs and border protection authorizes any personally owned weapons anymore. Some other DHS agencies, like ICE allow a limited selection of personally owned handguns but not personally owned long guns.
One argument I've heard from some DHS union and management officials regarding personally owned weapons has been that they don't believe the officers should have to pay out of their pocket for basic equipment. The liability thing it's really just a smokescreen. Any personally owned weapons would have to be from an approved list of manufacturers models etc. and would have to pass on armorers inspection prior to being placed in service.