I'm not sure how one could determine their therapist's attachment style in the first place. Maybe it would become obvious only if it was damaging the therapeutic relationship. It would be difficult to identify that, though, if the therapist didn't have the self-awareness and insight to see it happen and to own it. Otherwise therapy would probably get bogged down, seemingly for no reason.

I do think therapists can help with things they have struggled with in the past as long as they have their own issues under control. I would have fewer hesitations seeing a divorced marriage counselor than one who has never been married, for example. But if they were both well-qualified and insightful, I don't think it would matter that much either way. I guess the crucial thing is that they know themselves and have "done the work" on their issues.