I dont have my mouldmaking books to hand right at the moment.. So I can't check.. But I believe Latex cures by open air exposure, by forcing out the ammonia from the mixture thus causing the curing. Which is why you need good ventilation, to avoid ammonia build up.
Silicon spray or petrollium jelly are commonly used as a mould release agents which would interfer with any porosity of the the plaster mould.
If water moisture retention was to be of critical importance, for example, clay slip casting (Where the water absorption of the clay mix to the plaster was important) you'd use liquid soap as a release agent.
But Like I said my memory could just be dodgy, If you give me a day or two I'll be back at work and I check the books and say for definite.