I don't think there is any real issue using V4 skins for whatever. Just look at the galleries at Renderotica and other poser porn sites and you'll know what I mean. And I'm sure they use tons of skins from here too (because the best ones are sold here, and some good on Daz3d as well.)

As Ksanderson says, it's standard material in a release form, to ensure that the photos are not used in a way that could be harmful to the models, that's is exactly as it should be.

How the reworked third party skins are then used is not really an issue as far as I know..