1. How accurate is radar when they say "unverified"?
Don't know, but I suspect 500' difference in levels and you are in danger, 1000' and your probably OK.
2. Do VFR pilots really smash around in 8000' thick soup these days
Yes! On numerous occassions I have heard VFR aircraft depart into weather that I know must put them in the poo.
3. Given this champ went from being 2miles 10o'clock, to 1mile at 6 quite quickly, is it likely he was aware of the situation and "ducked" around behind while maintaining radio silence?
Maybe!
Dr 