Raises were recently released in our accounting system but not revealed to employees. Someone with access looked to see their raise ahead of time and compared their salary to others. This individual (angry) spoke with a "friend" in the office and was overheard by an "enemy". Things happened. I was told the (I'm sure) embellashed story in which my raise was revealed by the person who looked. Today, I found out that the "looker" was making inappropriate gestures and speaking in a vulgar way about the person who reported them HR/management to an employee I manage. Should I say something to my manager (who is also the "looker's" manager)?

Unless you think you'd enjoy a wee wee match with a skunk I'd keep out of this. If you think managers like whistle blowers you are mistaken.

I learned long ago that employee salaries are not a subject for discussion and I have often been in the position where I had access to that info.

I'm surprised this person was not terminated for this breach. But the fact is that HR is aware of the situation. Unless this toxic atmosphere affects your ability to do your job, then I would leave it alone.