I would start by calling Candidate Guidance (actually, have your DS do it) and asking if they'll give you the number for the Medical Officer. Your DS should state very clearly that he understands that waiver decisions aren't made until the entire package is in and USNA decides on an appointment decision BUT he want to know whether his condition is potentially waiverable so he knows whether to continue with the process.
Honestly, they may or not tell you if it's not waiverable -- IOW, it may be a VERY, VERY rare case that would be waived (i.e., 99% are not) but they don't want to say "no" outright. Not saying that will happen only that it's a possibility. He might also ask if the condition has been waived in recent years. I'm not saying the above will work, but it's worth the time of a call to see if you can get more info.
Your DS's approach should be -- "I'm not trying to back you into a corner or demand a decision on the spot. Rather, I want to know whether this is something that is doable if I'm a strong candidate or that there's no realistic shot so I need to move on my Plan B."
Also, whoever told you nothing would happen until everything is in is correct. USNA won't make a decision on a waiver until they are prepared to offer an appointment. However, they do know how frequently (if ever) this condition is waived. That can provide some guidance. For example, issues that are almost never waived include: asthma after age 13, ADHD or ADD that requires meds or accommodations, psychological disorders, missing one of two organs (e.g., kidney). Not sure where your DS's vision issue falls in the spectrum.