Dreadlords do, especially when their life is on the line.
As to the original thread topic: I don't think Vol'Jin is possessed. I don't think he's gone amoral either, he's just being practical. With a whole bunch of dead available it would make sense for him to let Sylvanas raise the dead as extra cannon fodder to save the living, especially if it meant he could finish his goal. Personally if I were him, I would have just let the Alliance go in first and set them up to fail, and then let Sylvanas raise the dead and finish the job. The whole event is going to weaken the Horde anyways, no reason to weaken the Horde further as well as leaving the Alliance at its current operating strength. Let the Alliance weaken itself in a failed attempt to capture the city, lower their moral, then unseat Garrosh, take the city, and you won't have to worry about the Alliance coming in after you take control because they'd still be butt hurt from their last attempt to take the city. All in all it's a win-win for everyone but the Alliance, who would once again get the much shorter end of the stick.