I was at SeaWorld a few days ago and though I didn't participate in the dining event, I was very close to it and could see and hear everything that was going on.
It's an all you can eat buffet with 1 or 2 actual killer whale trainers that "narrate" different facts about the whales. They also bring the whale out once everyone is seated with their food and it does a bunch of show things for you. No one was able to touch it, but it does swim up close to the see-through plexi glass that you are eating behind. You can ask the trainers questions and though they don't command the whales to intentionally get you wet, sometimes some water does make its way over the glass, which is about waist high on me (I am 5"4').
They assign you tables, some being right against the plexiglass and another row of tables behind that one. You don't get to choose where you sit as far as I know.
In the off-season, you can make your reservation that day to do breakfast or lunch. They were advertising it when I was there, and there seemed to be lots of room for it.
Have fun!