Can I use a gift card I don't have yet?

I'm getting rid of a few old Apple items through Phobio, and I've received some Apple gift cards from them. I need a new iPad, for which I will use the gift cards, and will send them my current iPad (aka "old iPad") after I get it.

Can I use that gift card and get the cost of the "old iPad" trade-in refunded from Apple after buying the new iPad?