Not speaking of AP 1 feet data We are currently on AP2 discussing a potential AP3.
The HD mapping uses the vision system in combination with everything else. It's not a pure radar map, that would be a ridiculous idea with the current radar setup. I haven't seen anyone else on this thread suggest it besides you. The article linked to was suggesting adding radar signatures to work with existing maps.
Radar signatures used for road mapping has shown to work in a few papers over the last few years.