"Move one target Orc unit from your kingdom or your quest zone to your battlefield. That unit must attack this turn if able."

If I play this tactic on one of my orc units in the window AFTER attackers have been declared, does my unit not attack because it is too late to declare him, or does this tactic make him automatically declared as an attacker as soon as it's moved into the battlefield?

The unit doesn't attack, because it is not able. Wolf Raider Assault doesn't move units declared as an attacker/attacking.

I guess he would be "unable" to attack if not declared as an attacker… Which is a sneaky move if you want him to defend the BZ next turn.

I've used this tactic before to move a unit from the quest zone to defend the battlefield. It's a nice surprise for the attacker.

Thanks a lot for your help fellas!