We have bought APs with gift cards on several occasions. The last time last year though, we were only allowed to use 2 forms of payment to buy them. I had tried booking online and wanted to use several gift cards but there was only an option for 2 methods of payment. I ended up having to call and ordered all 3 APs separately in order to use the gift cards - and I still could only use 2 forms of payment. On a couple of other occasions at both WDW and DL, we used multiple gift cards to pay for the APs, but that was in person with the CM scanning each gift card (and we had a lot of smaller ones so it was painfully time-consuming). I'd suggest buy the highest denomination you can in order to minimize the amount of cards you need for the passes. I have heard people on the boards here saying that depending on the CM you speak to, they might treat each gift card as a single form of payment and then you could use multiple, but you never know until you make the call.
Good luck!