Let's assume (although I don't believe it to be the case) that Ziem is one of the unmasked harassment complainants. Do the criminal charges filed against her by her former boss constitute unlawful retaliation under our workplace discrimination laws?
The answer is a qualified "yes."
1/ Title VII broadly defines "adverse action" for purposes of retaliation. The legal standard for an "adverse action" to support a claim for workplace retaliation is pretty low. How low? According to the Supreme Court, an adverse action sufficient to support a claim for retaliation is any action that would dissuade a reasonable worker from complaining about discrimination. I think it's fair to assume that a criminal complaint or prosecution would meet this standard. At least one court has held as much.
2/ Title VII protects former employees from retaliation no differently than current employees. In Robinson v. Shell Oil Co., the Supreme Court concluded that the term "employees" in Title VII's retaliation provision "includes former employees," allowing an employee to "bring suit against his former employer for post-employment actions allegedly taken in retaliation." Because of the similarity in language across the federal and state statutes, it's safe to assume this result applies across the board.
3/ Not all legal actions are retaliatory, even if filed for a spite. An allegation of a retaliatory motive is not enough to support a retaliation claim for filing criminal charges or otherwise institute criminal proceedings against an employee or ex-employee. In addition to motive, the employee must also establish that claims were baseless, frivolous, or in bad faith. Thus, as long as there exists a reasonable basis in fact to assert the claim, the law likely protects it is non-retaliatory. (The same holds true for a common law malicious prosecution claim for starting a criminal prosecution without probable cause.) Thus, if Watt had a reasonable and good faith basis to file criminal charges against an (ex-)employee, he'd receive a retaliation pass.
Regardless of the legality of the conduct, however, employers, please don't file claims (civil or criminal) against employees (current or former) who've engaged in protected activity unless you have a darn good reason to do so.
Unless you've suffered real, tangible harm, there exists the real risk that a jury will punish you for a perceived pettiness. Merely because a company may have a right to file a claim does not mean it will ultimately succeed on that claim. Indeed, the decision whether to pursue a claim against an employee or ex-employee who has engaged in some protected conduct must be carefully thought out, and not merely filed as a knee-jerk reaction. Moreover, depending on the strength and merit of the claim, its filing very well might result in more harm than good.
Or, in the words of another great philosopher, Eddie Vedder, "The best revenge is to live on and prove yourself."