Your hive is no hive at all, but rather the souls and bodies of the damned bound to your service with dark magic. Within this hive exists a variety of forms of undead, with purpose made horrors like the Vargheists, Bone Giants, & Necrofex Colossi, coexisting with more independent minded Vampires, strange beings like Wraiths, & cannon fodder like Skeletons.
While you can create many things ex nihilo purely from manipulation of Dhar, the true strength of your army is to turn the dead into your servants. This takes far less time, effort, and energy than meticulously creating your army from scratch. This allows you to snowball, with victories in battle leading to more corpses, which gives you a larger army, which leads to more victories. The more powerful your opponents, the more powerful your potential servants.
The dark magic animating even the seemingly independent minded Liches & Vampires is your own, meaning that their will is actually your will, no matter what. The Hive Mind is simply more obvious with your "simpler" minions, as they can do nothing without your command.