» Fri Jun 15, 2012 6:20 pm
On the Elder Scrolls wiki it says that the Shout is found in Soul Cairn, a new plane of Oblivion, and the way to Soul Cairn is through a portal in Castle Volkihar, which is the headquarters for the new vampires.
So as far as we can tell it's vampire only, although I'm sure that the Dawnguard will be able to find their way into Soul Cairn at some point. It'd be a shame if they didn't.