I booked a package through WDTC on our first WDW trip. Our travel vouchers were with Mears (shuttle).
I think WDW uses Mears for all travel. You might want to check out Mears web site. But I don't recall getting any kind of a price break/perk just because of having a Disney package. Our choices were to have the cost in the travel package, or not and figure out our own ground transportation.