Now that is an interesting one.
I wear a helmet both for skiing and for cycling, but not particularly from the safety point of view, as such. I was the first in my ski group/family to adopt a helmet after seeing stars after falling over on the glacier at Tignes. In terms of the risk in the activity, then a ski helmet is a more significant safety feature. I soon discovered that a helmet is simply the best kind of ski hat. Most significantly it gives you somewhere to park your goggles without them steaming up. I suppose it also gives you somewhere to park glasses when cycling, but they are not inclined to freeze over unless it really is a Rule 9 day!
It looks as if having a camera mount on your helmet makes a helmet more dangerous than not wearing one at all.
I take no sides on the debate as the safety issue is of little significance in both sports. A helmet will help you little if you ski over a cliff, or go under the back wheels of a truck. On the other hand, there is no point in wearing something potentially dangerous. But then, the risk is tiny, I suppose.