Rad alt didn't help that DC-10 in Antarctica. Nor will it help if you are flying towards steeply rising terrain. It would also help if you are actually watching it too. How safe would you feel riding shotgun while some guy flies at 200'agl while he watches the rad alt in poor viz ?? I think I would be asking him to please turn around !! Besides, didn't one of you say that one of the pilots already had an instrument rating ?? Did him a lot of good.
Dick our company ops-spec requires training once per year on low-viz ops. But it doesn't take long to do a couple of 360's in the a/c at 200' agl (or whatever height you feel comfortable at). Generally speaking when doing VFR recurrent training, we almost always have a little time to do company minimum airspeed, low-level flying. We pick a day with some wind, and in between autos, t/r failures, we go and do a couple of 360's at low level in the infield of the airfield. You have to do an hour's training anyways. Besides it's fun, and gets us ready for orbitting fires ad nauseum.
Cheers