Can some psychoactive substances really allow a person to have more access to universal knowledge?

I would say yes. there is a lot of deep introspection and self observation that can come from psychedelics. Its like putting a microscope on your consciousness and examining different aspects of it under an increased intensity of awareness. If you are obtaining knowledge of yourself, and you yourself being an active part of the universe, thats accessing universal knowledge is it not? Really the mind and psyche are infinite in their reaches. You can fit a huge metaphorical universe inside a very tiny head, all you have to do is fold it :).