The legal issue here would be intent. Of course it isn't illegal to have a voice that sounds like someone else, but Sam seems to have been arrogant enough to actually make their intent pretty easy to piece together with a small amount of public information. A lawsuit would allow discovery, and I wouldn't be surprised at all if internal emails even more explicitly spell out the intent to copy the voice from Her.
Proving intent is extremely hard and I always wonder how anyone that has enough power to pay attention let's their intent be documented. At least for Sam it sure seems to be due to a massive amount if arrogance.
However, the principle still stands.