Not sure anyone here could give you specific numbers. Based on anecdotal evidence, remedials are quite common. Remedials typically involve providing additional documentation about some condition and/or taking additional tests. It seems that most people come out fine after the remedials -- i.e., do not need a waiver. The remedial documentation/testing satisfies DODMERB and the candidate ends up qualified medically.
Only if you are DQ'ed by DODMERB do you need a waiver. Waivers are more dicey and, quite honestly, depend on your condition as well as overall competitiveness for an appointment. Some conditions are very unlikely to be waived and others much more likely. Some of it depends on the SA/ROTC program to which you're applying -- you could get a waiver for one but not for another. Most of it depends on the specifics of your condition, which is obviously very indiividualized.
Also, SAs typically won't go through the waiver process for a candidate unless they are likely to offer that candidate an appointment -- the reason is basically manpower/resources. Thus, some people may never know whether they would have been granted a waiver b/c, for other reasons, the SA decided not to offer them an appointment.