On a new build, the answer is a straight yes, because you would position the brackets in exactly the same way as on a battened roof. On a retrofit, when you are replacing the last course of slates, you can’t access the nailholes, so you would need to use the HallHook. On a battened roof the nail holes are determined by the battens. On a sark boarded roof, the nails should be in the right position but they could be in a different position.
If the nails are not in the same position on a battened roof, then the HallHook can’t work effectively as the lap could be compromised.