It's possible that he played a character in a film with a Confederate connection, but not specifically a Confederate soldier. To give you a more accurate answer, could you please provide more context about the movie you're thinking of? For example, you could tell me:
* The title of the movie
* The year the movie was released
* Any other details you remember about the character
With more information, I can help you determine if Jackson Rathbone played a Confederate soldier.