From what I understand vitaman B which includes actually a group of eight vitamins, which include thiamine (B1), riboflavin (B2), niacin (B3), pyridoxine (B6), folic acid (B9), cyanocobalamin (B12), pantothenic acid and biotin.
They aid in the central nervous system and it's proper functioning.
So this tells me that a good functioning nervous system would aid in any mental task, such as lucid dreaming.
BUT..If you are not deficient or lacking the source, then there would be no reason to take more
In all likelihood it will not have any effect at all.