You should still be able to claim it. I'm Canadian and it works just fine for me. Be sure to tell them what country you're from when you redeem though to be sure there are no issues. Also make sure the email you use on your account is accurate/works, because that is the email they will send the code to. Good luck
Personally I've never redeemed any of my points so far. But id imagine that the $20 voucher would be in the form of a code so amazon would convert it to whatever currency you are using on your profile.
They send you a code in the e-mail you signed up for gag with.
You insert that code into your amazon account.
That is how you obtain the gift card.
When you have it, you can search for whichever places deliver to where you live.
Wherever you are from, you should be able to receive the gift card.
I'm Canadian and I usually cash in my points for the Amazon Gift cards. I would definitely contact GAG about the gift card before you exchange your points, just to make sure you will be able to use it.
In my email to claim my points I indicated that I was Canadian so that they would know what currency to give it to me in as.