As it currently stands, owning alternate accounts is not a violation of the rules. Jeff Kaplan has explained more detail here:
He is also made a very in-depth post on the older forums. (Click here)
That being said I am all in support of Blizzard reevaluating their policies and working to find ways to make sure that anyone who is disruptive, no matter what account they are on, is prevented from accessing the game during a suspension.