In short: No, they’re not, largely because the largest subsidies go to the biggest, richest farmers. But even if they didn’t, Sallie James observes that farmers in general are richer than most people:
Farmers are wealthier (second graph from the bottom) and earn higher incomes (fourth graph from the bottom) than the average U.S. household. Their average debt-to-asset ratio is about 12 percent (third graph from the bottom), very low relative to the average U.S. household. Those should be the relevant data for any progressivity test.
America’s agricultural sector is very productive. And that’s an excellent thing and a real source of strength for the country. But it means that American farmers, though few in number, are pretty well off. They don’t need subsidies. But though few in number, they’re many in congressional representation.