Omar writes pretty much all of the music and he is a hard working nut. He doesn't need drugs to enhance his creative force, on the contrary, drugs would probably numb him and his creative writing.
I imagine Omar having the mind structured in a way that when he channels his ideas, the eclectic/psychedelic element is a natural feature.
In the same way it would work in Zappa's mind. The guy wrote sheet music but it was all awkward and counter-cultural. But the man was no on drugs.