Harvesters are things with KindOf = HARVESTER, ie workers, chinooks, supply trucks, toxic supply trucks.
I tried to make a Dune2 themed Zero Hour map.ini with a map in which harvesters brought to spice refineries by caryalls by script. When the harvester is dropped off at the refinery by the transport, it should then go and harvest spice.
The problem is, i cannot find a way to make harvesters belonging to AI players start harvesting. They will only harvest when they are built by the AI player's supply center/stash because when they exit they are somehow given the command to go and collect supplies. If they are spawned or dropped off by a scripted transport drop, they will just sit there doing nothing.
For the human player there is the script command to restart all idle supply trucks which does work (not only for truck but for all harvesters) so in the map the carryall drop is working for the human player. But this script command does not affect AI players.
If you want to see the problem you can download and play the
single player Dune 2 style test mission. You get a harvester dropped off by carryall and it will start harvesting spice without you telling it since i can script it to do that (shoot the spice bloom to the left of your base to make spice for it), but for the Ordos side i have to make their supply stash build harvesters since the carryall drops did not work.