if you have adsense on the front page of a site that has intenal pages with adult content - the front page does not have adult content and the internal pages do not have adsense - it is a myspace type site
Thier TOS says no sites with adult content, so I woud have to say it is probably not a good idea. Besides, the whole poit of that rule is to keep Google ads off imoral websites. What you want to do would violate the spirit of that rule, so I think you would get reported by someone.
If the internal pages are with adult content, does that imply the site is geared towards adult content? If so, the keywords of the site might inadvertantly retrieve "adult" AdSense ... which in this case is against their TOS as Google specifically mentioned there should not be any adult/porno on the site. It may not be a good scene to argue with them that the AdSense is on a page without adult content as Google will have the final say. Not worth to risk it.
yup, I saw lot of them too, some even put adsense on the page with adult/nudity content. This "hot-scenes" video is an example(this video has been online since 12/09/2005, look like a mistake of the site's webmaster).