Not sure if every council in Scotland is the same, but here we have the Disclosure Scotland scheme, and I don't think it's even mentioned on the Fife driver's application form - the council will get in touch with Disclosure Scotland and it all goes on 'behind the scenes' as far as applicants are concerned.
Which is all very well, but suppose someone is convicted of something immediately after a three-year badge is granted. If the applicant doesn't inform the council it could be three years until the council becomes aware, and if the driver has otherwise kept his nose clean during that period then it would be a bit of a nonsense to punish them via suspension or revocation, depending on how serious the offence is, as a few recent cases in Glasgow demonstrate.
Or the council might OK a driver who has informed them about something, then three years later Police Scotland object to the renewal when it comes up and they search their database.
So I suppose in principle it's only sensible to have frequent DBS checks, but how frequent they should be I'll leave to those down south, but as far as Scotland is concerned it all seems a bit daft