
In a recent reply from Karune on a battle.net forum post, he does in fact confirm that the alleged Zerg unit is that of the Ultralisk. He goes on to say in a later post that the unit has undergone some changes and to expect more on this and the Zerg soon!
Karune:
Nice find ;) This IS the new Zerg Ultralisk and you will be learning more and seeing more of it relatively soon. Also, the purple coloring shown on the Ultralisk's back are team colors and will change accordingly.
Also, I wanted to add that this is not the final version of the Ultralisk, as there is more visual work that has already been done on it, as well as new gameplay features we are testing on it.