[Baalz]

Blood hunting nations do surprisingly well under utterdark. Bloodhunting isn't effected by it, and demons all see in the dark. Use whatever gold you have to just recruit blood hunters and switch to just using demon troops. Depending on your research level, Hinnom has easy access to:

Those national lighting throwing demons.
Demon knights
Devils
Hoard from hell
Ritual of the five gates
Arch devils, Heli-however-you-spell-it, Lords of Civilization.

You've also got those quasi-imps in the conjuration tree for nature gems who are cheap, see in the dark, and work quite well after being buffed by bloodlust and weapons of sharpness.

Ps. Go tit-for-tat and put up Astral Corruption on top of Utterdark. Then stick your tongue out at him.