Picking up some of Porrohman's observations about the Cat C ILS procedure, an aircraft flying the outbound leg at 180 knots and initiating the base turn immediately on reaching D8 would remain clear of the Perth ATZ and therefore of much of its traffic - especially if it is being flown, as is more often the case, in a westerly wind that will blow the aircraft east as it flies round the base turn.
Leuchars' radar coverage of the western parts of the procedure at 2200ft is not bad, but it doesn't see much at 1000ft below and to the west of the procedure, where quite a lot of Perth traffic could be.
But I suspect the real issue with the radar coverage is not how much Leuchars can see, but the fact that it's provided from Leuchars and not Dundee. Once an inbound is transferred to Dundee the radar service ceases, and if the inbound is then doing the full procedure from the DND, any traffic info they might have been given by Leuchars immediately before handover will be old hat by the time they're flying the base turn close to Perth.
But looking at the incidents to Flybe Dash 8s this summer, I suspect they might have been driven by - as others have suggested here - crew inexperience with dealing with a non-radar visual circuit with lots of light aircraft. On one occasion the Dash reported turning base, having been advised he was No.3 to 2 light aircraft, and filed an MOR after Tower told him to extend to allow the light aircraft in.
If Dundee has a future as a commercial airport and future operations require radar, the best solution would be a joint deal with the MoD to position a radar serving both Leuchars and Dundee on the high ground behind Tayport/Newport. The Leuchars radar isn't being replaced under the NATS/Thales ATC contract for MoD airfields so there's scope for a joint purchase.