While pathogens are an issue, another issue is that of the area where releases are happening. While I recognize that you are attempting to repopulate, what is the cause of the lack of population in the first place. Certainly humans are a cause, but lack of food is the primary cause. Where there is a food source, a species will perpetuate, and, you may be familiar with the predator-prey cycles: predator successfully eats, population boom, starvation, prey population boom, predator successfully eats, etc etc. If you are releasing multiple offspring into an area where you found one snake, you may actually be forcing the cycle in such a way that is unnatural and makes it more difficult for the natural cycle to catch up. Think of it this way: 1 snake produces 10 offspring, half of which die. There are now 7 snakes (including the sire) in the area on the available food. Now, remove the gravid mother (affecting the population by one, not really affecting the prey), incubate the eggs and let them grow in captivity, now you have 11 snakes (assuming you keep the mother) where before you only had 7. The load being forced on the prey is more sudden, thus the impact is much stronger than it would normally be. To put it simply: 7 snakes to 10 prey items is a better bet for the prey than 11 snakes to 10 prey items, and by reintroducing captive bred snakes, you are offsetting the natural balance and possibly destroying the possibility of the population being able to recover in the area.