No one can prevent coaches from attending open meetings.. I think the objection seems to be to asking coaches to speak. That said, perhaps an answer would be a rotating schedule. It seems to me the benefits outweigh any drawbacks. Off court communication between coaches and officials is a good way to foster healthy on-court communication.
Sounds like this particular A.D. is having a power trip, and probably thinks he lost a game because the officials were favoring a coach who'd spoke at one of those meetings. Perhaps it should be suggested to him that he attend a meeting where one of the other coaches speaks before he make a blanket judgment like that.
Or, you could make him an offer he can't refuse.
