Notarization doesn't blanket block all access to private APIs; but the notarization process may look for and block certain known accesses in certain cases. This is because notarization is not intended to be an Apple policy enforcement mechanism. It's intended to block malicious software.

So in other words, using private APIs in and of itself isn't an issue. Neither is it an issue if your application is one that serves up adult content, or is an alternate App Store, or anything else that Apple might reject from its own App Store for policy reasons. It's basically doing what you might expect a virus scanner to do.