IIRC a few years back Discover had the 5% deal for hotels, so I paid my KTTW charges at my resort with DS and got the 5%. As far as booking your package with the DS card, yes, most TA's have Disney process your card, but it's Walt Disney Travel Company that is paid, and I'd think it's considered a trip/travel booking and not a theme park purchase.
I think (no proof!) that if you used Discover in the actual parks, at a cart or store or ticket window for example, that it could be considered a Theme Park purchase, depends how DS has those classified. Sometimes credit card classifications for vendors can be a little quirky.