All RHS rock sliders are required to be compliant with and are compliant with ADR 42.9 'External Protrusions'.

There are no other ADR's relevant to rock sliders.  Compliance with this ADR is legally required but that is all.  There is no such thing as government certification, the government does not offer any engineering services in relation to aftermarket accessories and ADR's.  Manufacturers are free to state that their products meet the ADR's and that they 'certify' that they meet the ADR's, if they meet the ADR's.  If statements like this were made and they were false that would be false advertising and the product would not be compliant.  Various manufacturers will make various claims which can be misunderstood or misleading.

ADR 42.9. EXTERNAL OR INTERNAL PROTRUSIONS
42.9.1. No vehicle must be equipped with:
42.9.1.1. any object or fitting, not technically essential to such vehicle, which protrudes from any part of the vehicle so that it is likely to increase the risk of bodily injury to any person;
42.9.1.2. any object or fitting technically essential to such vehicle unless its design, construction and conditions and the manner in which it is affixed to the vehicle are such as to reduce to a minimum the risk of bodily injury to any person;
42.9.1.3. any object or fitting which, because it is pointed or has a sharp edge, is likely to increase the risk of bodily injury to any person;

Rock sliders provide extra protection in side impact collisions.  It is theoretically possible that in some side impact collisions the fitment of rock sliders to a vehicle with side airbags could cause the side airbags to deploy fractionally faster than if rock sliders were not fitted, and this may be desirable to match any change in deceleration.  This could only be tested by crash testing entire vehicles.  I am not aware of any rock slider manufacturer undergoing this level of testing.  Various manufacturers will make various claims which can be misunderstood or misleading.