We just got back from a great stay at GC and we got tickets at the hotel. BEWARE, they did not initially give me Hoppers, even though I asked. When I questioned them again about hopping (before the transaction was complete) they did finally give me the correct tickets. Remember, Calif. is not used to hopping between parks and many employees don't automatically offer it, because it's never been an option here before.
If you just ask if you can go to either park, they will say "yes" because you CAN go to either park, however, it is just one park per day.
As I understand it, they have tickets for use at just one park, tickets that can be used at either park but only one park per day, and they have hoppers that can be used at both parks each day.
Just be clear that you want the hoppers and know that they are a bit more expensive than the flex passes.
Enjoy life and great vacations!
Chri