I also ran into a "no" on this. Best Buy's support concerning subscriptions is lacking to say the least, but after 8 transfers over two different sets of phone calls I received a confirmed answer that you can only use this on Pandora Free accounts. I'm especially disappointed that the Overview section of the page states "Pandora Plus subscription code" but this is not what you're purchasing. You're instead purchasing an activation link that has Pandora reach out to your Best Buy account to tie together this subscription.
I get to find out if there's an expiration date because instead of getting a deal I bought an albatross that hopefully still works in May 2022 when my existing Pandora Plus subscription expires. The part of the product page that is accurate is "Non-returnable"