Play at the beginning of your Battlefield phase. Action: When you declare an attack against target opponent, that attack is against all of that opponent's non-burning zones. Defending opponent may declare defenders from all of his non-burning zones. This effect lasts until the end of the phase.

When you play All Out War can you attack a legend? If so, does this attack count as against all of that opponent's non-burning zones?

From the last thing I heard, it would be an attack on the legend through all non-burning zones, yes. You might want to submit this as a rules question though to get something official.