If wife's attorney serves her list of potential witnesses 3 days after the deadline, is it valid?

I depends on what the trial judge says. If it causes you some prejudice you may have an argument, but I would not assume the failure to be timely invalidates the document. Further if the certificate of service is dated on the last day, there is a three day mailing rule, so it may not be late aftera ll. You might want to hire a lawyer ot advise you of strategy.