Good therapy involves having a good theraputic alliance.
It means you and your therapist are allies.
It makes sense that it would feel confusing, weird, even triggering, to find out that your ally, is also in a therapeutic relationship, a theraputic alliance with perpetrators.
My trauma therapist (in fact all three that I have seen) have also worked with perpetrators. Intellectually, I'm glad for it. Intellectually, I think it's a good thing and it doesn't make me think of her or the the rosy any different, and maybe even makes me think more of her.
Emotionally, yeah, it's confusing and unsettling.
I really encourage you to talk to your therapist more about your reaction to it. It is my guess that they will be able to help you sort through it. Talking through my own emotional reaction to that helped me to be able to trust the therapist even more over the long haul - and I don't trust easily at all.