You simply cannot compare the nutritional needs of snakes with those of humans. They are not equal.
Snakes get all of their nutrients from the food they eat. Humans do NOT get all the nutrients they need from the food they eat. Our diets are so flawed that we need vitamins and supplements to stay healthy.
Is it essential? No.
Will they survive without it? Yes, they will thrive.
why not? because there is not one proven need for it in snakes.
If you want to spend $10 to inject your rodents with vitamins, go for it. But I am telling you, you are wasting your time.