“Our analysis shows that the two voices are similar but likely not identical,” Berisha said.
They also point out the main differences between the two voices in the paragraphs below this quote. I do believe that they hired a voice actress and that they didn’t train on SJ’s voice, or at least not entirely. However, I wouldn’t be surprised if there was big push for finding a voice similar to SJ’s voice in Her, no matter how much they deny this.
I might be wrong, but I think they will probably let the OS handle the biometrics offline, which means that they won’t have access to your biometrics, they just work with cryptographic keys. Otherwise it doesn’t make sense, as apps usually don’t have direct access to the fingerprint reader. It will probably be similar to how a passkey works.