Gromit. That lil guy is always on it when his owner has no clue.

Siri was originally based off real VAs, I’m unaware if they’ve moved away from that since

Allowed by who? Whether it’s legal or not depends on jurisdiction, I would assume, and whether it’s moral is up to each individual’s morals. It’s likely if you’re cloning someone’s voice that they often are someone that makes their living off their voice, be it a voice actor or celebrity etc.