My very first LDT was on a standard CZ125 with road tyres. 2017 Exeter. I was treated exactly the same as every other competitor largely because the Marshall's are looking for feet down and don't know you have special dispensation because they haven't been told or are just unaware of what tyres you have. To be fair I've never been that competitive and I was elated just to have finished on that bike. It was very hard work and I thoroughly enjoyed the whole event. Met lots of new friends one of whom I consider a great friend Rick Howell.
I don't know how, unless you told each Marshall in advance you are on road tyres, they would ever know. And even then if you we're footing up the lane it would be up to interpretation of how many dabs you took. Sounds like hard work for the Marshall's to me.
The point is...Marshals [Observers] are required to
only record, what they see.
It is for the results crew at the end of a trial to determine whether that which has been recorded, is applicable to that competitor, or not.
The Results crew will be perfectly aware of any special dispensations to apply.