As I understand it, just a regular cutter bar and a round baler should work for harvesting hemp for commercial fiber. Too bad the knee-jerk government folks won't let farmers raise it since it's a good commerical crop, grows even on poor farmland, and should be competitive even against cheap foreign production.
As for the drug trade, marijuana almost has to be hand picked as the buds and new leaves are the ones with the most THC in them. Sure, you can use the whole plant, but then it's only about as effective as smoking a string of baling twine.