Having only scanned the thread, a couple of thoughts:
I admit most of my ideas are heavily inspired by WH40k Tyranids. If you don't want to go into that direction at all with your Hive, I understand.
Is there any kind of "hive mind" mechanic planned?
I'm thinking "pets" here (pretty much a copy of Warlock Pylons, excluding losing control of workers), connected to the Queen that you place around the hive which constantly dish out slight(!) attribute and speed buffs to all units passing by, to create the illusion of an Overmind/Queen that gives focus and purpose to all your shambling hordes and maybe a kind of solitude-debuff when outside of the Hives' range for an extended amount of time. This ability could also be added to specific units as a form of overseer-creatures with a stronger connection to the Overmind/Queen.
Also ZERGZERGZERG. Units are weak when alone, but the more other hivecreatures are close the stronger they become. Could simply be a (limited) stacking buff hivecreatures cast on each other.
Evolution.
Fight dwarves -> gain dwarf corpses -> eat dwarf corpses -> get better at fighting dwarfs.
I vaguely remember there being some kind of issues with corpses being substituted with bones in reactions, so maybe use souls+(generic) meat instead.
The upgrades could be various: like self-buffs when in proximity to dwarves, or a poison/acid spitting syndrome that only affects dwarves, or permanently transforming into some kind of caste/creature with natural weapons made of material that heavily damages dwarves, but works less well against other creatures (like moon/shadesilver for good/evil creatures). So you get Uriszzzzzzzt McDwarfremover who only comes out against dwarves and Urizzzt McDe-Elfer who's geared towards fighting Elves, etc.
I have a couple more ideas, but no time now.
Should I keep posting or is this not a direction you guys want to take?