Rat!!!!,
Canopies can descend in holes with a circumference far less than that required for an aircraft. So in theory a 900ft cloud base is not a problem as long as there is a hole for them to descend thru.
I have also been involved with CASA approved cloud jumping operations. In conjunction with appropriate aircraft, primary and secondary radar, trained ground staff and radio calls it is a safe and reasonable operation. Just because Mr Gypsy moth doesn't want to listen to (or worse still not carry) a radio doesn't mean parachuting ops should not be approved.
Can I suggest a call to the operator with your concerns, or failing that a call to your local FOI would be a more appropriate channel. From my skydiving days a call like that would be taken very seriously.
