Confirmed, DISNEYPAL (or DISNEYPAL30) doesn't work on MagicBands. Edit: It does give you free shipping if your cart is over $85 (Same as the code: SHIPMAGIC).
Ive gotten discounts on them. Its just certain codes work on certain things. I bought an Aulani necklace and it awhile to find one that would work on it but finally I got one.
Regarding Capital One (I have the Quicksilver card btw), I enabled the feature that looks for discount codes while browsing websites. I happened to be looking at bands earlier today when I saw the notification from CapOne. I have an email confirmation about the discount, and I just need to click on the link in said email to activate it.