Server-driven UI rendering and React-Native isn't mutual exclusive though. Server can still render a React-Component-tree-like structure that will then be used in the client to render the actual component in react native. This gives you ability to make some UI layout/theme adjustment from the server, which is good for A/B test. Doesn't means it goes back to rendering every view from the server on every interaction.

"Facebook app has a big enough surface that it makes sense to have different rendering strategies for different use cases."

That's an odd statement. Playing mix-n-match with rendering strategies without a very clear UX justification for doing it is an invitation for designers and mediocre product people to indulge themselves at the expense of the overall UX.