It couldn't hurt to put down your ethnicity if you're a "minority". I'm heading for NAPS, and I've noticed that a number of my soon-to-be classmates are minorities. I'm a registered Cherokee Indian (even though it's only a fraction of my blood), and now I wonder if putting that down on my application had anything to do with my being selected for NAPS.
Oh well. I suppose that's because Congress holds the purse strings and wants to appear "fair"...
The subject of diversity can be more tangled than a can of fishhooks but I believe the bottom line is if USNA doen't think you're qualified you won't get an appointment.
Cheers...