Unless they cultivate to the Ghost King Realm and refine a True Body—which, much like the Golden Core of a human cultivator, acts as a spiritual energy conversion furnace capable of transforming spiritual energy on a large scale—
By the time they reach the Ghost Emperor Realm and possess a Dharma Domain, heaven and earth become the source of their own power, making the distinction between spiritual energy and ghost energy far less distinct.
Of course, near ghost veins, the combat prowess of a Ghost Emperor still receives a certain boost.
Chapter 257