Radar is usually always available on the ADRs (subject to the usual limitations), but the ADRs base levels don't go down to the surface.
Radar wouldn't have helped the Loganair pilot as he was conducting a non precision approach with no radar service available. It's a recurring theme in Loganair fatalities, simply due to the nature of their operations and the airfields they were using at the times of the accidents.
The cumulo granite in Scotland is very unforgiving to people who make mistakes in IMC, as the number of crashes (many with bits of wreckage still present) will testify.