When my Mid attended CVW, and again when she was a host, there were only a couple of attendees per company, so ~60, give or take some. I believe that she asked to be a sponsor, so that would be a form of screening.
What are your odds of being paired with someone who loathes USNA? Well, ~80% of an incoming class makes it to graduation these days, so I'd say your chances are less than 20%. By the time you get there, those who immediately regretted their decision will have been long gone, although there may be some who have decided to leave at the end of Plebe year. My guess is that the chances are even lower than that, because I doubt that the CoC would knowingly pair CVW visitors with Plebes who are having serious issues.
OTOH, while there, you probably will hear griping, even from Plebes who have no intention of leaving, and you will find Plebes who are "less than happy." It goes with the territory. Some days are better than others. It's better for all involved if you see how current Plebes are dealing with life.
In addition to USNA1985's comment that life in March does not equal life in October, also remember that life in company 6 is not the same as life in, say company 10 or 26. Even within a single company, things can change a lot even from one semester to the next.
Go in with eyes open, ask questions, and prepare yourself to make the most informed decision (if offered an appointment) possible!