You can buy them dried peas, depends on if they eat them or not, but, the peas should be fed as a treat, not a diet. They need a full diet full of nutrients, treats should consist of up to a very small about of the diet. I don't know the exact percentage, I feel like I heard 10% somewhere, but i don't know for sure.
You can feed them the dry stuff, as long as there aren't any additives. They will likely prefer the fresh stuff more then the dry. The peas shouldn't make up more than 10% of their diet.