Is it possibly to make a foaming sugar body scrub with an organic liquid soap base? and if so would you still need to add vitamin e and a preservative?
Vitamin E is to prevent rancidity of oils, so if you don't plan on adding oils, you won't need to add it (it's also oil-soluble, so it won't mix with water).
Anything that might be introduced to water should use a preservative.
You will need to read the ingredients on the bottle of organic natural soap base you plan to use and make that determintaion in accord w/ what is and is not alread in it.
Without knowing what is in it already & what else you plan to add to your recipe there is no real answer for your question.