Not sure how to answer that. The social security law doesn't say that you CAN have a trust. A special needs trust is more like a loophole. It's not specifically in the law, it's something that finds it's way around the law.... without violating the law.
Guess I'd be very specific with them about wording. I'd say that I am not giving money to my son. I will set up a special needs trust with the advice of an attorney. IF that special needs trust can provide something for my son within the law according to my attorney than it MAY do so.
Frnakly, I don't see why to mention it at all. It's something in the future. You meet with them to discuss the past or the current, not the future.