I used to raise a lot of rabbits, they did well on good alfalfa hay, rolled barley and poplar branches. (Trembling aspen). Rabbits in the wild prefer to eat the bark from aspen, and it also serves to keep their teeth trimmed and give them something to do.
No personal experience with hemp meal, but it’s a byproduct of oil extraction, a significant product. I expect it would be good feed. Hemp is a tall and dense crop, which will compete well against weeds. But the seed is carried on the top part of the plants, and the stalks are very fibrous, which will complicate harvest and processing the waste.
Here the established practice for harvest is to straight cut the field with a combine harvester at about 4 ft / 1.4m, then cut and bale the stalks after. If not needed for fiber the stalks still have to be removed from the field or tillage will be impossible. So the work to obtain the seed is higher than grain or soybeans.