I think there's a Poe's law type thing going on here: looking at behavior alone, it's very difficult to tell the difference between a concern troll and a tentative ally with the right ideological background. That's probably especially true for cultures like social justice that use a lot of endogenous concepts and terminology: within those movements, any concerns that don't speak the language are going to pattern-match to "enemy" on linguistic grounds and suffer from the corresponding horns effect.

With that in mind, I suspect they exist but are pretty rare.