DH and I did Dolphins in Depth this past November and we loved it. If you search you'll find my review. It was included in the plan we were on at the time, so we felt it was well worth it

You get to rub them down and give them signals in waist-deep water. I've never read anything about the dolphins *not* interacting with you, but since it's impossible to force an animal that size to do something, there is a possibility that they'd decide they weren't having anything to do with it on your particular day. But since there are 2 or them, chances are very high that at least one of them will be happy to see you

We booked a few months before our trip. The number you call is 407-WDW-TOUR.
With all of that said, on our next trip we'll be trying Discovery Cove. We want to *swim* with the dolphins this time

And there there are so many dolphins that the interaction is guaranteed. It is expensive though - over $200/person. For that, the interaction had better be guaranteed
If you just wanted to touch the dolphins, I'm pretty sure there's a place in Sea World where you can feed them - you have to buy the fish, but it's a lot cheaper than either Dolphins or Discovery Cove.
HTH
