My understanding is that faxes are no longer looked at at some, if not all of the resorts. I know that for DVC, Member Services has said more than once that they do not even read faxed requests. Touring Plans apparently now emails the resorts instead of using fax. It would make sense then that the resorts are unlikely to accept faxes - but each resort is operated slightly differently, so mileage may vary.
The preferred method of making requests is to have it noted on your room reservation.
Steve