I just found out in Skylanders Spyro's Universe website a proof that Sparx will be in Skylanders ! link.
I don't if he'll be a playable character or some sort of item but he'll be in the game for sure.
However, it seems he may be only available in a Limited Edition Adventure Pack : link
Not sure about that though.
And they called him Spark instead of Sparx.
What's up with that ?

Edit : After close inspection, I wonder if they didn't misunderstood the Limited pack category with the Dragon's Peak category. If it's the case, Sparx may be available in the Dragon's Peak pack.