As a data point for the walmart offer, phyical gift cards appear to be triggering the offer if bought online. I was a few dollars short on an online order a couple days ago and added a $5 physical gift card to see what would happen and got the email last night saying I had redeemed the offer.

I think I'm going to buy a $40 gift card online once I'm sure the offer posts, I don't shop at Walmart much but they can be used at sams