yea but if he had his aperture wide open, ISO as low as possible, and shutter speed maxed out, an ND filter would help a little. I often shoot on sunny days with an open aperture and I'm forced to use an ND filter; that's not even on snow.
It wouldn't hurt to darken the skier a little bit anyways, it would give the pants a more rich color. So if the whole image was darkened a little to bring out some detail in the snow and maybe darken the skier a little too, that wouldn't be the worst thing. If he's not going to be using a strobe, he is going to have to probably accept some noise in his image when he fixes it in post.
i did forget about the 10.5 thing though, good catch. so all of this is kind of irrelevant anyways
The joy I get from skiing...that's worth dying for. - CR Johnson