Rentals no. Subscriptions, yes. The difference is this, a rental becomes no longer usable
once the rental period expires. A subscription on the other hand, already purchased content
remains, even after the subscription expires. Think in terms of magazines for example. You
subscribe to a magazine, with that subscription, you get x number of issues. If you choose
not to renew, you don't lose those issues, you still have them. You simply do not get new
issues. There is a kind of gray area with subsciptions though. If the subscription is to a
service, once it's expired all access goes away. Such subscriptions are not allowed through
in-app purchase.
In your specific case, it sounds like you're selling content that though consumed in the app
is actually external to the app. This would be better served via an account based system
on your website.
Keep in mind, what Apple does via iTunes has no bearing on what we as developers can
do.