would there be any advantage to also mounting a CB?

That was the question. I would only depend on a CB near a highway that has considerable truck traffic. There are some people who use CB radios for local communications to keep up with their buddies but I would not count on CB for an emergency. It certainly would not have helped the Kims. If you want to get found it sounds like PLB is the way to go. I don't own one yet but I will. I am also a ham. Unless I had an HF rig in the vehicle, I would not count on much help from Ham radio in the Kim's situation. The 2 meter band is line of site. I doubt that there was a repeater near the Kim's.