Managers and supervisors really ought to be trained on this topic. The problem is that oftentimes the person who has filed a complaint continues to work for the same supervisor he/she has claimed did something wrong. It is only natural for a person who has been accused of wrongdoing to be spiteful towards their accuser if they think the claim is unjust, or if they think the accuser is a liar. So, that makes it even more important to let managers know that time will reveal the truth about the employee's claims--and if the manager did nothing wrong, it will play out--BUT they can't give into those urges to exact some type of revenge on the employee in the interim. That can be easier said than done.
If at all possible, the employee should be reassigned to another supervisor so that there is no direct day-to-day relationship between the employee and the manager named in the employee's claim/complaint. But if that's not possible, it's essential to make sure the manager understands the danger of retaliation. If possible, use real life examples of retaliation verdicts (BLR's newsletters have cases in them all the time) where the employee ultimately lost their claim of discrimination (or whatever) but won big money on retaliation, all because some manager couldn't resist 'getting back' at the employee for making a complaint.
Of course, in cases of co-worker retaliation, it can get a little trickier. Managers should be sure to be on the lookout for that too and be sure to discipline anyone who engages in retaliatory behavior. Looking the other way while co-workers retaliate is also a no-no that should be communicated to all managers.