I have been reading this thread, but not yet contributed. I would think it is very clear - if this is the safest way to lift your dog then you would do it, wouldnt you? If the dog is supported in another way in addition to the scruff then I dont believe it would hurt them and if it did they would wriggle/yelp. It would hurt more to not have a safe grip on the dog and to then drop it. The dogs in question are not scared of their owners and we all know they are much loved members of their families so their respective owners would not do anything to intentionally hurt them in any way.
They are all clearly very well trained, fulfilled dogs.
I dont lift mine this way but that is because I am not in a situation where that would be necessary - you guys dont do that to lift them in and out of the bath