Yes, they're both owned by the same company or at least run by the same people. The models they work with overlap a lot, but the pictorials don't as far as I know. But like I already said, I've only seen a few pictorials from METmodels and I wasn't able to find them on MET-art, so at least the pictorials are different or I missed the pictorials in question.
Anyway, since I've been a member of MET-ART, I can confirm that they have a lot of picture sets to offer (& movies as well to a lesser extent, but I wouldn't bother if that's what you're after...), but I can't say the same about METmodels, simply because I don't know how much they have to offer.