I dunno if its a park hopper or not. I honestly dont think it would be because its like $90 for a one day park hopper and like $50-60 for a one day single park ticket. There is always a catch to everything and Disney will want to save money if they can, so I would think it would only be for one park. But even still if your paying like $50-$60 at the gate for that ticket and they give you a GC for that amount, thats a nice chunk of change to spend on yourself if your asking me.
But I believe that you have to register all your birthday's on the
Disneyland website and Disney sends you a confirmation 2 weeks before your trip to the park. You take that to the park with your ID to prove your birthday and they issue you a card as long as you are there a day before, on, or a day after your birthday.
If it is the amount of a park hopper, then I would definately look into seeing if it can go towards tickets for the parks for all your birthdays later in the year.