Force ghosts are only shown appearing to Luke and Yoda. The fact that Leia doesn't seem to acknowledge the ghosts at the end of RoTJ and Han rides through Obi Wan's ghost on his Tauntaun seems to imply that they couldn't/didn't see the ghosts.
However, the fact that Han and Leia haven't been trained to use the Force doesn't have to be the only explanation for this. It could also be that the ghosts can choose to manifest themselves to specific people. But since they are "Force" ghosts, it makes sense that a person's sensitivity to the Force would also be a factor.
On a side note, regarding Luke recognizing Hayden Christensen: going all the way back to ANH, the movies repeatedly establish that a Jedi is able to "feel" someone's presence without needing to see their face. Vader knows that Obi Wan is on board the Death Star without needing to see his face, because he can "feel" his presence. Vader knows that Luke is with the small group of rebels who sneaked onto the Forest Moon, because he can "feel" him (while the Emperor, intriguingly, can't). In both TESB and RoTJ, Leia can "feel" Luke's presence without needing to see him.
So based on all of that, it's actually very well established that when Luke sees Hayden, he would be able to "feel" the presence of Anakin even though his physical eyes don't recognize the face. After all, one of the very first lessons Obi Wan gave Luke was blocking his vision with a helmet that had the blast shield down and telling him "Your eyes can deceive you, don't trust them."
Okay, I'm going to go violently throw up all my Thanksgiving dinner now. The insertion of Hayden into the ending of RoTJ is so hated by me that I can't even bear to watch it, and I'm beyond disgusted with myself for defending the logic of it in this post. I've also contradicted my previous posts, because elsewhere I have said that the insertion of Hayden makes no sense because Luke wouldn't recognize him, and I'm super reluctant to take that back, regardless of what I've said here. I feel like I just helped Palpatine kill Mace Windu and now I'm dropping to my knees crying, "What have I done?"