I'm pretty sure it'll work the same way as WoW CE's
You can still redeem any CE version of WoW for the in-game pet n shit.
What if I purchase the Diablo III Collector's Edition?
If you decide to purchase the Diablo III Collector's Edition when it's available, and then choose to add your Collector's Edition license key to the Battle.net account associated with your existing World of Warcraft Annual Pass promotion, you will receive all of the benefits associated with the Collector's Edition, plus receive four months of World of Warcraft game time which is eligible towards your 12-month subscription commitment. After you purchase the Diablo III Collector's Edition you just need to input the product key into the Battle.net account associated with your World of Warcraft 12-month commitment and that account will then receive the next 4 months of World of Warcraft game time for free. For example, if you already had a month of game time on the associated World of Warcraft account when you input your Diablo III Collector's Edition product key, it would then be 5 months until your next subscription payment was due.