When the FAQ states that Ents cards are considered as attacks for political purposes, does that mean Rohan is activated and goes down one? I can't think of any other thing to conclude from this, because Isen is already at war.
No, it means the Nation that is attacked is affected politically, as usual. In the base game, it has no practical effect as you say, but in the Expansion any Shadow Nation may be the subject of the attack.
"War is much more fun when you're winning!" - General Martok