They used a sound-alike and had her sing one of her songs. I believe that's a different precedent, in that it's leveraging her fame.

Imo Sky's voice is distinct enough from Scarlett, and it wasn't implied to _be_ her.

Sam's "Her" tweet could be interpreted as such, but defending the tweet as the concept of "Her", rather than the voice itself, is.

Does not the 'her' tweet give away the game. Aas you said, it was a midler impersator singing one of midlers songs. In this case they have a voice for their AI assistant/phone sex toy that is very much like the actress that played a famous ai assistant/phone sex toy. Even if he is taken as meaning the concept it's very very damning. If they had, instead, mimic'ed another famous actor's voice that hasn't played a robot/ai/whatever and used that would that really be any better though? Christopher Walken, say, or hell Bette Midler?