After all, Scarlett was playing a role in the movie (lending her voice to it), and they wanted to replicate this acted out role.
If the intent alone mattered, OpenAI should be in the clear. More so if they never specially instructed this voice actor to “sound like Scarlett”.
On the other hand, Sama reaching out to Scarlett directly over a number of times doesn’t lend a good look. Perhaps they felt that Scarlett has already done it (acted out as a voice agent they were trying to bring to life) and she would truly understand what they were going for.
Maybe, it was also a bit for marketing and the buzz-worthy story it might generate (“OpenAI worked with ScarJo to create their life-like AI voice. Scarlett was also the voice behind the AI in “Her”).
However, I’m not a lawyer and the the law could very well view this more favourably towards Scarlett.