Here is my take on wearing a swastika even if it is for a movie costume. I airsoft, and I wear alot of tactical gear and camoflauge, sometimes I even try to replicate a certain group, however, I would not ever wear any patches or symbols, if you have not earned them. Even if they are your grandfathers swastikas he kept since that time. To me, if I was in the military and I see somebody wearing a unit patch or a rank, I would be offended seeing as he has not earned that. Now, here is the grey area, since it is just a costume, it would be fine to wear it. After all, it is just a costume right? I mean, you really didn't kill 6 million Jews did you? The reason why I say this is a grey area is that if you are just replicating a nazi uniform then, IMO people at con's or halloween are still going to like it, even without the swastikas on them. If it is Tom Cruise's character in the movie, the knock yourself out with swastika's.
And before anybody here thinks that I am ignorant for saying wear them, I'll have you know that I know alot about world war II and the world back around that time period. I know alot about many genocides, I have studied these things so I can have the knowledge today. I do not support the Nazi party, nor am I saying this to purposely offend Jewish people. It's just a costume.
Edit- Also, like someone before me said, dont sugar coat your costume if it is a movie or game replication. You either make it or you dont. You arent trying to feed anyone with that symbol of hate, but rather making an accurate costume.