some will say yes...some will say no. i cannot answer the question for as long as you have to activate it but some people have reported that they had to go to guest services to activate their pass and show it later at the front desk to avoid being charges the regular rate. i have been asked for it on all of my trips. the first trip, i hadn't picked it up yet and they said ok and never asked me to bring it back. my second trip they asked to see it. my third trip they asked if i had one but didn't ask to see it.
as far as the discounts go on the park stuff and restaurants, to my knowledge you have to have an actual annual pass. I can't imagine that you could use the voucher. also when you pick up your voucher, it is actually a one time pass to get into the parks and you are supposed to go to guest services to trade it in for the annual pass.
i wouldn't even consider not activating it but maybe someone else can give you more precise answers. in my opinion, i would purchase it even if i had already bought tickets if i thought that i would get another trip in. i got 3 trips in on mine and planning the 4th before it expires and it has more than paid for itself.
