Klaus could summon the hosts if he likes- however, they are a peaceful people by nature and are not built for fighting tactically like many of the citizens of Hadriel might be. They are fairly squishy and cannot operate most weaponry, however, they will attempt to protect Klaus and fight off any Null that endanger him- likely through swarming the offending Null and dragging it to the ground, rendering it unable to move by deadlocking it with their spindly tendrils.

Klaus is welcome to summon unappable ghosts through the door, though we will put a soft limit on the number he'll be able to bring in. Alternatively, he could summon monsters that the door has previously brought in and were killed.