Having looked at the UKAIS page for the Dundee ILS / LOC approach, whether the base turn was made at 8 nm from the NDB or as a dme range is not really the issue.
To me the issue is the descent starts inbound at either glideslope capture cross checked with 6.7 dme, or if a Localiser procedure at 6.7d which is a dme distance, so the dme should be tuned and used.
I can understand tracking inbound to the NDB using gps especially as it is on the coast and may have some errors but once at the beacon, surely you fly the procedure using the correct aids?
Of course we are assuming that there was a working ils receiver in the aeroplane!
Just my tuppence worth.