IMO, it'd be good at the very least for takedown purposes. If Petruz suddenly decided that all the posts using their models should no longer be on e6, I'd say the site should respect that (here's hoping that never happens). With that said, tagging them as an artist seems off, and copyright might not work if the modeller also does their own art. I'm tempted to suggest an entirely new tag category for collaborators (could maybe also include sound design, voice acting, backgrounds, etc.), but that sounds complicated and I'm not sure it's worthwhile.
Thoughts?