The situation is this: artillery and cavalry are ordered in the left flank. Cavalry battles first and opponent plays charge when charged. As a result the cavalry must retreat and block los for the artillery. The artillery reposition is played. Is that allowed?
Well, I don't know for sure, but absent further guidance I would play it that the ART unit could move up to 2 hexes using the Reposition card. I think that would also apply if the CAV was bounced by a flag roll from a unit that forms square, and the ART unit was part of a combined arms attack with that CAV unit.
........Anyway, we always played that a unit ordered to battle is considered to have battled, not only in the case you point out with the Tactician card, but same thing if a unit was order to fire and the enemy unit retreated due to an earlier combat or was eliminated.
To answer your question specifically, the artillery unit does not have to battle in order to move 2 hexes. If it was ordered to battle and some action caused it not to be able to battle, it is still considered to have battled in reference to the Tactician card.