It won't be for a blockout ticket per se. I don't know how Disney could let me volunteer for a free ticket voucher and then not give me a one-park voucher just because I also HAPPEN to have an AP. Then I would still have to pay $25 or so to upgrade to a hopper, though, so my savings would be pretty low.
I suppose it is possible that they wouldn't let me get a free day just because I have an AP, but that would be pretty low of them, IMO. With the birthday promotion, I'm pretty sure you could use it for a free ticket on your birthday if your birthday fell on a blockout day. (I know there's a day or two in June that are probably blockout days and that you can't use for your voucher, but I don't think the day I'm looking at is one of those. Worst case, I can get the FPs or possibly the pin figure I don't really want.
)
Which indicates to me that since I don't have a VALID pass at the time, I can use it for a one-day, one-park ticket.
So I should be able to upgrade to a hopper (again, at additional cost, but probably $20 less than a $45 blockout ticket).