We have seen park photographers in the lazy river (taking pics of people underwater with the sunken treasure chest, as well as by the waterfall at the entrance to the aviary), in the Freshwater Oasis, and in the aviary. In fact, two of my favourite pics from our DC days have been the ones taken the Freshwater Oasis and the lazy river (but we love those dolphin photos, too!).
For the dolphin swim portion, we had "formal" pics posing with the dolphin (DH alone, DS alone, me alone, DH & I together, and DH, DS & I all together), each of us kissing the dolphin, and several of each of us having our "swim" with the dolphin. Usually there were multiple shots of each pose. I think, for our family of 3, we had about 40 pictures from the dolphin swim portion of our day, plus several others from throughout the park.
Don't forget you also get a 6 x 8 family photo as part of your admission, which is taken by park photographers as you arrive (just after you check in).