[throwawayReply]

You can have both, if it's just randomness then you can have shared seeds which the server will verify but the local client can sample too. If they de-sync then the server wins, but the client can feedback quicker before the final response from the server.

I suppose that would enable further cheats such as not wasting pokeballs on ones you know will fail by peeking into the future.

The throw itself is client-side though, so I suspect it's already possible to cheat with "perfect throws" every time.