On day 1 of most NROTC programs the participants, programmers and scholarship recipients alike will "Line up" and complete a physical assessment -varies between Marines, Navy options on standards. And if they meet the standard they continue. in some programs by the end of day 1 a number of programmers are no longer in the program.
As others above noted, it likely varies greatly from 1 school to another. Your focus if you go the programming or scholarship route should be to come in physically and mentally prepared to survive your first year. Really it matters little how many people are invited or can show on day 1. It may not be hard to show up on day 1, but look at the size of programs on day 1 to the number of people who commission. Often, many do not make it to commission - not everyone makes it through NSI (for scholarship kids), the advanced calc and physics (for Navy option, not marine), the fitness tests, drug tests, alcohol arrests, etc, etc. . . Look at the number of Navy National Scholarship winners who scrubbed prior to the end of their first, second years. This isn't easy. Sadly too sometimes people in their Jr. / Sr. years also scrub (and after day 1 of sophomore year, they owe the scholarship back).
Just my opinion but I think the programmers may in fact have less "slack" to fail than scholarship students, so the bar is higher. Specifically for instance at one school a few scholarship young adults failed the run on day 1 and had time through the semester to improve. The programmers who failed the timed run/ overall fitness test or were late on day 1 (yes, believe it or not people sauntered in 15-30 mins late at 4:45AM - I saw it w my own eyes - couldn't believe it) were walked over to the ROO of another branch and were done with the Navy - at least for that semester. Also, doing well as a programmer can mean you "pick up" and get a scholarship (sideload).
Hope those details may help you. Good luck.