Yes, if you check out the GAD details on the GAD section of the WDW website, you can see that the price of a 1-day ticket will be applied to AP purchase.
If you are renewing, I'm fairly certain you can't use it for your renewal if you are outside your "renewal period" (which is ususally 30 days before and 30 days after the date your AP expires. For example, our AP's expire at the end of this month, but we are not going to be at WDW until June (well past the 30 day post expiration window). From what I've seen, you need to get your ticket at will call, go through the gate and then go to guest services for the upgrade. So I think we would not get the renewal rate if we waited until June to buy the AP's with the GAD voucher.
I've been keeping my eyes open to see if anyone else has this situation. You need to weigh the renewal rate (plus the extra 3-mos they are giving on renewals right now) vs. just buying a new AP. I think you end up saving $40 or so using the GAD voucher if you can't also get the renewal rate.