As far as I know they are all taking reservations; I have made them before. You will have to call the restaurant directly. The dining line does not make these.
I am not sure about any discounts. However, they do offer the Safari Club which I joined in November. It is $15.00 but I got a $10 gift certificate and will recieve 10% off of future purchases.
When I went to Rainforest in February they had had a price increase and I was a little disappointed.