Knights of Tezoth

You'd have to ask Revan, but doesn't the Prince's Cloak display the attack from Aragorn's Horn as a spell on itself?

As a normal attack, yes.

So misses and crits from the horn are also possible?

well, it turns out that's the case

And what about Ferlutz's Shield? If the horn counts against it, does the shield reflect damage to the spirit in Arandor?

The lizard needs to recalculate the pipes. It's possible the horn missed.