I've used vitamins on snakes for years, but somewhat sparingly. I started with avian vitamins before the reptile vits were common. As far as I can tell there has been no problems with my snakes as a result. Breeding females got calcium supplements here and there.
About eggbinding - probably not just about calcium. In fact, may have little to do with it as far as snakes are concerned. It is likely about failure of the keeper to provide an adequate environment for the female to want to lay her eggs. Some females may be more picky than others and retain eggs if a suitable nest site is not found. That is what many who have kept snakes for many years surmise.
Lack of muscle tone may or may not contribute. Small cages are so prevalent in the hobby.
Also nobody knows if eggbinding happens in the wild or how often if it does.
And lastly, there may be something else that eludes the experts.
I would like to see data with incidences of eggbinding and the types of caging used. I would bet small cages with little ventilation and a very tight temperature range factor highly in the incidence. Just a guess. The only times I've had eggbinding was in sweaterboxes, never in larger cages, but it is not nearly enough snakes to draw a certain conclusion (but I will anyway.)