This particular area of law or even just type of "fairness" is by necessity very muddy, there isn't a set of well-defined rules you can follow that will guarantee an outcome where everyone is happy no matter what, sometimes you have to step back and evaluate how people feel about things at various steps along the way.
I'd speculate that OAI's attempts to reach out to SJ are probably the result of those evaluations - "this seems like it could make her people upset, so maybe we should pay her to not be mad?"
Even if this did go down the way you suppose, once they realized the obvious similarities, the ethical thing to do was to not use the voice. It doesn’t matter if the intention was pure. It doesn’t matter if it was an accident.