What I would be looking for is something like the following:
Dan tattled on Ken to Ken's boss.
Dan positive tattled on Ken to Ken's boss.
To further clarify what I'm looking for... It's not so much that Dan tattling on Ken is a good thing, but more that what Dan is tattling about is positive.
Dan tattled on Ken that Ken was being a jerk
Dan ____ on Ken that Ken was being helpful
In this context, whistleblower, duly reported..... none of these really fit the bill. I have my own suggestion that I will answer with to give a better idea... anonymously praised