Neither of those will have 3D capabilities or be able to use any of their spatial APIs. Seeing regular 2D photos/videos on a VR headset is nothing special.
I didn't hear anything like cryptography being used to restrict 3D images to only ones from your device (or even only other Vision Pros), seems like an enterprising studio could just buy one to record with if there's really no way to get existing videos onto it (is there an eye-contact issue with existing content? seems like this could solve that if there is).
Where porn can be played, it will always be played. They teamed up with Unity3d to make app development easier so I guarantee someone can make VR porn with that and find some workarounds to get it working