Ada Hand Cycle Rules

Trying to get info on whether a cycling event can ban hand cycles. Last year some members of our cycling club went to a ride in Hattiesburg, MS. At the start of the ride our club ride director and previous president was told he was not allowed to take part as he uses a hand cycle due to physical limitations that confine him to a wheelchair. This gentleman regularly does century rides with our A group. We were told at the start that on the advice of their attorneys and insurance company he could not take part although he paid his entry fee. The person in charge required him to sign a statement, if he wanted to ride, that said he was not a part of their event. Is this legal under the ADA guidelines?