Google has never served rich results for adult content. However, they also won’t be demoted for containing rich results markup, it just won’t be shown due to the adult nature of the site.
SafeSearch filters determine whether or not content is eligible for rich results. If content doesn’t pass a SafeSearch filter then it can’t be displayed. If a large majority of a domain’s content doesn’t pass SafeSearch then Google will filter out all content and not include it in rich results. Ideally you need to keep adult content on a subdomain or a seperate domain so that Google can identify the difference. Otherwise you run the risk of your whole site being excluded from rich results, even if you only have a small percentage of adult content.