Revenue sharing on forums and on adsense being placed on proxified pages is 2 different case. Adsense being placed on the forum if allowed by the webmaster is allowed by Google generally known as forum revenue sharing as the content is contributed by the user as well, however again it is only allowed if the webmaster allows it.
I dont think Myspace, Facebook, or any other websites allow you to place adsense on their websites. Therefore with this scenario in mind, adsense ads are not allowed on proxified pages as they are considered placing ads on web properties that do not belong to you.
In conclusion, it is a widely known fact that adsense is not allowed on proxified pages as Google has made it clear by banning publishers who actively do that.