You will earn eBucks on the payment made with the gift card and with the CC. So yes, earning eBucks on your eBucks... boggles the mind hey?
not sure if true - i have spent about 12k in vouchers the last few months. only earn i get is when i actually have to pay in a difference (and then you only earn on that difference - eg the amount that goes through your bank account which the ebucks guys can see)