The only discounts that I have seen is available to Sea World Passport holders, and thats only on occasion. Other then that, I haven't seen any discounts.
We were getting travel info from our local AAA and asked for anything they had on Discovery Cove, meaning brochures and things - turns out, they offer discounted passes!! You have to go through them to make reservations (naturally) but you save about $13 a person, which is better than nothing!!