The majority of them, I agree, seem to be limited in intelligence. But a few of the Grimoire cards depict the Wizards in particular of having vast intelligence, even beyond the scope of a Ghost's capabilities. The World's Grave library is said to hold more information then should be physically possible, and their ships employ wormhole technology that other races haven't been able to emulate or equal. While most of the Hive seem like mindless, screaming pawns of death, there is a distinct intelligence behind them.