Yes, there is a documentary running on Discovery Wings at the moment regarding the aforementioned Weather Pilots.
Three types:
One set fly above 'feeder clouds' spraying silver iodide into the clouds.
One set fly above the clouds with flares, putting the stuff into the rising moisture, forming the clouds.
One set fly directing near to the epicentre of the storm (and the documentary footage shows some crazy turbulence +/- 6000 ft updrafts!), spraying similar chemicals.
The effect of these is to remove the oxygen from the air (correct me if I'm wrong), meaning there is less oxygen to form water....and thus hail. So, hail DOES come down, but in smaller pieces.
You're right, it was a result of insurance companies asking for the flying to be done, to avoid expensive insurance payouts.
This area near Calgarry is known as hail alley, and they get football-sized chunks come down weekly.
The job looked fantastic though - turbulent flights every day! The aircraft took an inevitable battering however, with bits falling off everywhere.
The best thing was that environmentalists couldn't complain - they weren't affecting the weather patterns...just the size of the hail.
There is a great photo of the trials for this thing, where someone flew a figure of 8 above a cloud formation. The photo of the resulting cloud shows where the silver iodide caused the clouds to 'collapse' in on themselves.
Incidentally, does anyone know - isn't silver iodide the stuff they use on camera film?