Advertising is between site owners and advertisers directly, so I suppose so since the only advertisers you wound get are the ones interested in advertising specifically on your site. Although wouldn't really want a bunch of porn sites in the list of available advertisers... So should probably make an option so a site owner can tag their site as adult and then it would hide it in the site list.
The "adult oriented site" option has been added to the edit/create site page. Essentially this allows adult sites to use the system, but advertisers would need to find out about the site from the site itself, and they won't show on the public list of sites to advertise on.