I've promoted this site through various channels for a while. I use their FHG's at my blog.
the result? signups.
I've talked to guys in email about legallity and seen them quoted several times about legality and while i can offer no garuntees i do know that they say they do not promote condone underage photography. they do not attempt to make sales for people looking for that kind of content. they do not welcome that kind of marketing. they shoot only consenting adult models.
so for whatever that's worth that's cool.
look at this gallery for example:
http://hosted.met-art.com/generated_.../922213/24180/
that's some of the most incredible content in the industry imho and i love listing it. its amazing softcore.
2257 exempt? Unlikely. but i'm not hosting it on my server anyways so who cares, as long as i've been assured they're of legal age.
They're not guiltier about marketing to the folks looking for just over the border 18 folks than many, many programs who are owned by folks right in our kneck of the woods.
If you're uncomfortable marketing the 'just recently 18' crowd might want to take a good look at some of the programs you're promoting. I can think of several sites offhand that have these types of sites in their programs.