I'll make this blog quick. No.
I get it. You're proud of what you are doing, and the uniform is really really handy. Add to that, some people actually go to a costume store and BUY a karate costume, so what's wrong with using a real uniform.
I'll make this simple. Are you just pretending to be a martial arts student, or are you actually one? If a police officer showed up at a Halloween party dressed as a Police Officer, everyone would feel sorry that he didn't have time to go home and change after work. If a 3rd grader went to a party dressed as a 3rd grader - I mean, what's the point?
The reason people BUY karate costumes is because they haven't EARNED one.
Through your training, hard work, discipline, and accomplishments - you have earned your uniform. Every wear-spot, yellow sweat stain, and colored belt. You don't have to pretend to be a martial artist; you are one.