Usually, in today’s paranormal world every ghost hunter sees the terms as synonyms. The cultural definition is that a cemetery refers to a large burial ground, typically not associated with a church. The first citation in the Oxford English Dictionary for graveyard comes from 1767, and a graveyard is typically smaller than a cemetery and is often associated with a church. It is part of the churchyard.
Graveyard = Church
Cemetery = Usually no church, and bigger.