Unsplash make them free to use, but can't guarantee they fall within the full licence terms. They haven't replied, but I don't think I've misinterpreted it.

They don't have model release forms on the site. On Alamy, where I contribute, no photos of people are released to commercial buyers unless they have model release forms.

It's entirely plausible that the photographers have indeed got model release forms for commercial use, but Unsplash isn't checking, so they're not in a position to verify the release or whether it's good for commercial use.

Artwork, images, and photography that's captured within the shot would probably be covered by the artwork clause.

It is ambiguous but I don't think I've misunderstood. If they reply, I'll be sure to let you know! In the mean time, I did change it to the exact wording yesterday.