I have not seen any sources which explicitly state that FaceID doesn't work the same way as TouchID does, but perhaps it's the lack of specific details in the iOS Security Guide [0] that might have led to this assumption?
In fact, FaceID solely relies on the IR camera to do its work. You can cover the front-facing (normal) camera and your iPhone would still unlock successfully. Conversely, the newly touted Animoji feature does NOT rely on the IR camera at all, as evidenced in this iPhone X review [1] at 11:40. It may be the case that the OS don't have access to it.
I can’t swear to you that this is exactly the same depth data that FaceID uses. Maybe it’s been downsampled in some way that makes it safe to give to apps, without enabling attacks on FaceID. I think I’d be a bit more willing to believe that if Apple’s Security docs actually said that. To me it seems more likely that the raw depth maps are available to the app processor (and to apps!) because the SEP isn’t powerful enough to perform the recognition task on its own.
In fact, FaceID solely relies on the IR camera to do its work. You can cover the front-facing (normal) camera and your iPhone would still unlock successfully. Conversely, the newly touted Animoji feature does NOT rely on the IR camera at all, as evidenced in this iPhone X review [1] at 11:40. It may be the case that the OS don't have access to it.
[0] https://images.apple.com/business/docs/iOS_Security_Guide.pd...
[1] https://www.youtube.com/watch?v=9Ca8zWJOlFQ&t=700