That's a good question. On the one hand it says on pg. 72 in the little grey box that a hero comes under the same effect as his formation when they are targeted by a spell. Since the Ringwraith is a Spirit it could make sense that he would take those extra hits even if his formation aren't spirits.
On the other hand though it says if the target enemy are Spirits you would add the additional hits, but you're not targeting the Wraith you're targeting his formation. So would the Wraith be the only one subject to both the courage penalty AND the extra hits even though the actual target was the orcs? I dunno
Guess it just depends on how you interpret it. I could see it either way.