The residue can be a problem . I think it important to follow the grain of the roller crimper so the drill doesn't get balled up .We planted an irregular field the other day and had problems with the thatch rolling upon the coulters making big balls.. First time for that. Seems long straight fields don't have problems. Also I have mowed hemp and not had problems drilling to it. Lastly the drill can have a hard time cutting the hemp if going across the grain. The stuff is very fibrous .I know it will plant it, I think some are concerned about residue for the next crop. I don't think it would be an issue I was saying. There are a lot of acres in a similar mix around me this year do to all the prevent plant acres.
Another thing I have done in the past is to raise the deck on the bush hog as high as it can go and mow the hemp when it is 4-5 ' tall. From what I have read this causes the root system to be much denser yet the hemp doesn't get so tall.
Not familiar with Grand Pa Ray's mix but yes what I plant is similar except I add iron clay cow peas which do very well in the south. They end up climbing up the hemp and can actually bend it over sometimes to the ground by late summer. This may be what happened to the field where I had troubles as the hemp wasn't in uniform lines for drilling to