The ABCs do make some profit from moisture... They buy moist at a discount, and blend it with anything dryer than spec and sell it at spec. This practice probably generates roughly a 0.5% boost to revenue depending on the weather. This would be incredibly hard for farmers to capture because it requires buying from places with a wet harvest and places with a very dry harvest.
Actually, a lot of elevators make most of their profit on moisture management. Being able to nail a 15% M on a 125 car train can bring in a lot of money. There are farmers who do dry their grain before they bring it in, but gas dryers are expensive.
That really depends on the contract. A much more costly problem is Moisture. Its rather costly to dry grain.