I *think* it is supposed to act as an anti-oxidant for your superfatted oils. However I don't know if it really does or not or whether it is affected by the lye.
No matter what oil you use, it depends on your superfat.
Why don't you use a small amount of Vitamin E (like 5 % of your total recipe), put that in the soap calculator and up the superfat a bit, like maybe 7 or 8%) My belief is that even if you add it at trace, it will still be saponified.
Vitamin E is good for the skin, it has regenerative and healing qualities, and is good for mature dry skin because it is readily absorbed.
It would make a good ingredient for your soap.
Not to me, just in lotions and stuff..... It is really bad if I have a sunburn or windburn, If I use anything with Vitamin E on my face then my eyes swell so much I can't open them!