If talking to Oxford or Brize GA aircraft can be routed through D129 when not activated as both have Letters Of Agreement that allow that. When gliding at Weston is taking place you can be routed through above the cable launch height with a general warning of levels gliding up to (generally cloud base).
D129 DA status for parachuting at Weston is believed to be a legacy throwback to when they used to Barrage Balloon jump; it is the only drop zone in uk with dedicated DA status.
Hope this helps.