Service-to-self underlies dark personality traits

[Stranger]

Ohh, I misunderstood!

Do you happen to see any kind of good out come existing when a person with those tendencies has them revealed to themself in a therapeutic approach?

It depends.

They may have been aware of it already, but justified it to themselves ("it's a dog eat dog world", etc) in which case it won't make a difference.

If they were not aware of it before, having it revealed will force them to make a choice: admit it and have to do something about it (this is the only healthy choice), or engage in some form of an ego-defensive maneuver (e.g., denial, anger at the person confronting them, minimizing the severity of it, etc.)