Since the payments would have to be made through the App Store platform (unless Facebook forced the user to subscribe through a web browser) Apple would most likely be profiting though.
Could Facebook make it happen and profitable in a way to get around Apples rules? I think so... I think Apple would change the rules shortly after though...
AFAIK the rule is that users can subscribe to a service/product outside of an app and use their account's status on the app, but if the user wants to subscribe from within the app they need to go through the App Store subscription service.