I've always used purchased content and have never had any problems with sponsors (large or small) but I've always written my ads in such a way that it was clear to the surfer they would be going to a new web site.
If I was advertising a single model web site I would more than likely use a banner which showed the model and use text that made it clear to the surfer what they could expect to find if they clicked on the ad.
As long as the advertising isn't misleading and it's made clear to the surfer that they are going to a different web site, it shouldn't make any real difference. If, however, you design a gallery as if it's part of the sponsors site and imply that the content of the gallery is a free sample of what is to be found in the sponsors site, then yes, there's a problem.
Just my thoughts...
Regards,
SF