It's completely non-sanctioned. Blizzard's Terms of Use have the following section:
Ownership/Selling of the Account or Virtual Items.
Blizzard does not recognize the
transfer of World of Warcraft Accounts
or BNET Accounts (each an “Account”).
You may not purchase, sell, gift or
trade any Account, or offer to
purchase, sell, gift or trade any
Account, and any such attempt shall be
null and void. Blizzard owns, has
licensed, or otherwise has rights to
all of the content that appears in the
Game. You agree that you have no right
or title in or to any such content,
including without limitation the
virtual goods or currency appearing or
originating in the Game, or any other
attributes associated with any
Account. Blizzard does not recognize
any purported transfers of virtual
property executed outside of the Game,
or the purported sale, gift or trade
in the “real world” of anything that
appears or originates in the Game.
Accordingly, you may not sell in-game
items or currency for “real” money, or
exchange those items or currency for
value outside of the Game.
In other words, trading in-game items for any sort of external reward (be it real money, Second Life money, Facebook credits, or anything else) is prohibited.