The problem here is that someone inside of OpenAI wanted to create a marketing buzz around a new product launch and capitalize on a movie. In order to do that they wanted a voice that sounded like that movie. They hired a voice actor that sounded enough like ScarJo to hedge against actually getting the actor to do it. When she declined they decided to implement their contingency plan.
If they're liable is for a jury to decide, but the case precedent that I've seen, along with the intent, wouldn't look good if I were on that jury.
If her customers can get sued for using her voice, then this voice actor can never get another job and can never get paid again -- all because she happens to sound like ScarJo. That seems unfair to the voice actor.
If you had a voice like Scarlett, and you were hired to create the voice of an AI assistant, there's no legal problem - as long as the voice isn't marketed using references to Scarlett.
However, in this case, the voice is similar to Scarlett's, AND they referenced a popular movie where Scarlett voiced an AI assistant, and named the assistant in a way that is evocative of Scarlett's name, and reached out to Scarlett wanting to use her voice. It is those factors that make it legally questionable, as it appears that they knowingly capitalized on the voice's similarity to Scarlett's without her permission.
It is about intent, and how the voice is marketed. Voice sounds like a famous person = fine, voice sounds like a famous person and the voice is marketed as being similar to the famous person's = not fine.
It is not a clear-cut 'this is definitely illegal' in this case, it is a grey area that a court would have to decide on.