It was in ADR20, but this was cancelled in 2003 and replaced by the general safety recommendations of ADR42. ADR42 does not make any stipulations regarding tubed rims with tubeless tyres.
However, tyre fitting businesses have been banned by their Liability Insurers from fitting tyres to tubed rims without using tubes on the grounds that ADR20 set the precedent that the practice is unsafe and exposes the business to undue liability. Ask your local tyre fitter if they will fit tubeless tyres to tubeless rims, and they probably won't (and quite a high proportion won't. I only know of one place that still does, and that is only after you tell them it is for an "old farm trailer" or such, not for road use.), they will cite liability insurance as the cause for the ban. Despite the practice being perfectly within the letter of the law, depending on their level of interaction with their insurers, most will not be willing to void their policy cover just to please an insistant customer.
One tyre fitting business I am familiar with had the unfortunate experience of a workplace accident that killed an employee, and were dragged through the wringer by their insurers and Workcover, and today are exemplar in following rules. You know the lines painted across the workshop doors that say "No admittance to workshop"? Most places treat that as optional depending on your attitude. Cross that when dropping line off tyres and the whole place stops work like a wild west saloon when the black hat walks in, until you comply with the shouts to get back outside. They've got the message good and proper. What the insurer says, goes.
