Futher, specific to your question: the court doesn't care one way or another. They'll take his testimony if he wants to give it, and they'll have it even easier to make a decision without. A civil court is also unlikely to be in a position to grant any immunity.

Neither google nor the court care about the conflicts of interest on the defendants' side. I'd even agree with you that at-will employment is evil, and legitimately pleading the 5th shouldn't be enough to fire someone. But specifically in this case, Lewandowsky could be fired even if he were employed by the French government – he could then sue himself, and the findings of the google/uber trial would probably determine his claim of wrongful dismissal.