I preface this with....I can only speak towards USMA, as that is only academy we have visited, looked into, and talked to people at:
By "Preppies", I am thinking you mean High School Preparatory Schools that offer a high level of academics and sports, but don't usually have a JROTC component. If you are speaking of high school "preppies", then they would need a nomination just like anyone else, in any of the categories available to them. If they are in a Military Prep School (JROTC or ROTC program), such as MMI, GMI, etc, then they could very well get one of 3-6 nominations of their ROTC Cadre. I don't see how they would fall under "Regular Army" if they are in high school??? Be careful with 32 CFR, USMA is specifically governed by Title 10 US Code as it was explained to my son and I by admissions. 32 CFR 573 Section 6 ONLY applies to active members of the armed services, not prep schools of any kind as far as I can tell, plus 32 CFR only lists 2995 total cadets, when currently there are over 4000 at USMA, so be careful using these figures. If they are attending USMAPS, that is a totally different animal....if they complete the program they usually will be offered an appointment to USMA.