Corn snakes don't need to be brumated for reproductive success. I've bred them without brumating them and have had 100% of the eggs be good and viable. It appears that you can be just as likely to get bad eggs without brumating them, because, of course, there are many variables. But environmental cues, like reduced photoperiod etc., are often enough for spermatogenesis and follicular development to run its course.
Brumation is hard on snakes. Every year, I hear of someone who lost a suboc during or just after brumation. As snake owners, we offer our captive charges very little choice of how and where they will spend the brumal period. Usually, it's sitting on aspen in a 36" x 18" enclosure. In the wild, I am sure that snakes take many environmental conditions into consideration...things like substrate dampness, substrate texture, substrate dryness, maybe even substrate pH, amount of visible sunlight, darkness, draftiness, stuffiness, temperature, and on and on down the line... these are probably all considered by a snake about to enter into winter dormancy. There is one huge macrohabitat with plenty of microhabitats to choose from. Now, I know that wild snakes have to compete with other snakes and avoid predation, etc., but you get the idea that there are probably more suitable overwintering locations for a wild snake than for a captive in a sweater box.
If something is bothering the captive snake for the 2 - 3 months during brumation (e.g., substrate or air that is too dry or too damp), and it can't do anything about it to make a difference in its situation, I can see how that can take its toll on the health of an animal, especially an animal that was already immunosuppressed before it was exposed to yet another unsuitable annoyance or condition.
Sooo...I've given you a drawn out response, but I think you should continue putting weight on your snakes, if you have any question as to whether your animals are fit enough or not, in that regard. Because if there isn't enough weight, it definitely won't matter if they've been brumated or not.
Cheers,
DR
Suboc.com