Nobody is going to care about MEPS as soon as you leave there. It's inprocessing. That's all. The whole "you'll get pulled out of Basic if you lie about anything, we have detectives..." is ridiculous. That said, it is on you to be honest about everything and maintain personal integrity. But no. Nobody is going to "bust" you at Basic Training for having a couple scars. The Drill Sergeants will never see your Medical Records, and nobody will even read them if they did. Reception processes 1000 soldiers a day. Nobody is reading anything in your packet except what station you need to go to next.