I'm 99% sure thats fine, trading cards are routinely sold on ebay and similar sites, I'm sure that a trading card that happens to have a loot code on the back falls under roughly the same guidlines

Buying TCG stuff is fine, they were engineered like that in the first place.

Short answer: Yes

Longer answer:
It's okay to sell TCG cards because you own them. When you purchase the commodity, the seller turns over the disposition of the article to you. A seller only has first sale rights, meaning they can only control the product until they sell it... however you do not own WoW. What you buy is a copy of the client software. What you buy is Blizzard's permission to use their game client (the material form of this permission are the reg codes on the CDs), and your subscription pays for Blizzard's permission to use their game server - you own none of the virtual items. Since you don't own any of it, you can't sell it.

A TCG card is an IRL bearer-owned item. You can buy, sell, or trade it because it is just that... an IRL item.

At one point, it was not allowed to sell a card's loot code for in-game currency. That was changed, shortly before they changed loot card rewards to be BoE or BoU. Now you can buy/sell an in-game redeemed item for in-game currency as well.

Just last night on my server, though, there was someone trying to sell WoW game time for in-game currency... still not allowed.