No and sort of yes. The money in the account can only be used for Disney purchases. If you buy airfare directly from the airline or even through one of the discount travel websites, you can't use the DVA to pay for it. But if you're buying your souvenirs ahead of time from the online
Disney store, you can use the DVA account number as a form of payment in the gift card line.
It be refunded to the original form of payment or you can request a Disney GC for the overage.
This isn't a credit account. It's a "savings" account that pays zero interest and is not subject to the same terms that bank accounts operate under. If you neglect to add money, you just have less money in there to apply to your vacation payment.
It is harder to get your money back than with a bank account. There are limits on where it can be spent. It ties your funds up in Disney money. That means that, unlike a real savings account, you don't have immediate access to cash if you have an emergency.
But on the plus side - it allows you to combine a lot of Disney GCs in one place so that you can make an online payment for tickets or room reservation. And, you get a $20 Disney GC for every $1000 you spend from the account.