My two cents: The most widely accepted definition of a terrorist is someone who intentionally targets non-combatants with violence for political purposes. The shooter at Fort Hood, by contrast, was targeting uniformed combatants. In that sense, he was not a terrorist. So what was he? A traitor, a man who wore his country’s uniform, and killed his fellow countrymen in the service of his country’s enemies.
Is there a reason we no longer use the word “traitor”? Maybe it’s time to reintroduce it into our vocabulary?
There is this complicating factor: Soldiers acting as peace-keepers, e.g. the U.S. Marines in Beirut who were suicide-bombed by Hezbollah in 1983, are considered non-combatants. So attacking them does count as terrorism.
By contrast, the troops at Fort Hood had been (or were to be) fighting al-Qaeda and the Taliban. They were combatants, even if they were not on a conventional battlefield.
I think our working assumption has to be that what took place at Fort Hood was an act of treachery and asymmetrical warfare, an act — in the eyes of the perpetrator — of jihad on behalf of Islamist terrorists.