It's EXTREMELY rare for them to allow you to pre-pay on your account with a gift card. And even if they did, you have to link a CC to enable magic band charging.
I pay for my full trips with gift cards and we go every year. I can tell you in all the years since the magic bands started, I've had *one* CM who loaded a gift card to my room account on day 1 as a pre-pay. It's really not a hassle though to use them -- We charge throughout the day with our bands (with mobile ordering now, we pay directly with gift card - save the card number in a notes file on your phone and just copy/paste!) using them for food, shopping, whatever. Then every evening when we come in from the parks, as we pass through the lobby I stop off at the front desk and pay whatever the current balance is (the concierge can also do this for you if the front desk is busy with check-ins). I've only ever had an issue where they had already charged my credit card one time (and that was because we had a very large spending day at Epcot Food & Wine) but they offered to reverse that charge and let me pay with a gift card. It took a few extra minutes but that's been literally once out of dozens of times.
You do want to have a physical gift card with you. They can usually run a digital one, but it's a lot more work for them and not every CM knows how to do it. I carry one physical card with me and transfer to it from my others as needed using the disney gift card site. That way I'm not carrying around thousands in gift cards. I have at least 2 other physical cards on the trip, usually locked in the room safe. That way if something happens to my "main" card, I can immediately move the funds off it to one of my back ups.