Correct me if I'm wrong on this, but aren't counselors bound by some kind of a non-disclosure agreement? Also, these counselors do hear some odd things from day to day. I'm sure wearing diapers/"ABDL" is not that far from center. I remember my college psych prof. telling me about this child she had who would essentially mess into a cup because that was the only thing they could control.
Point I'm making, you shouldn't have to worry about if a counselor is AB/DL aware. Find a counselor that you are comfortable seeing, fits into your budget, and can get you the type of help you need. He or she will not have any qualms about AB/DL.