The director wanted to heighten the outrage of the audience over the injustice of forcing the Japanese into camps. In order to do this he couldn't have the audience feeling that the Japanese thought of themselves as anything other than loyal americans. Therefore, in one scene at the camp for example, the Japanese are listening to the popular music of the time and not to traditional Hogaku. The point being that these Japanese-Americans were as american as any other of our next door neighbors and should not have been treated as an enemy. The first rule in movies is that the scene drive the film, not the music.
Music is an adder, for mood, for tension, for identifying a character, or whatever.
The music follows the visual. The music is lead by the visual. In conclusion I would like to add some random thoughts about the intersection of Hollywood and Shakuhachi. It is my personal belief that there are two Shakuhachi's. One Shakuhachi is actually an attitude which comprises a body of work, Japanese music and in particular Honkyoku, and the other Shakuhachi is merely an instrument.