The truth is there were some signs of his existence like that earthquake happened when killer was late, but you dont know for sure. Both endings dont make it clear. So its up to player to decide.

I highly doubt a sociable man would desecrate random corpses in a ritualistic manner for no reason that coincidences with the strange ground liquefaction.

Zimforth is real - he's in El Paso, Elsewhere too

I'm leaning towards real because of the missions that require you to find the odd man out of the group. Knowledge of the existence of those people seems to be rather supernatural to me.

There is a purple light that appears every time that Zimforths speaks to Ralph that is also present during the earthquake. It's also too conventient that this earth shattering natural disaster happened right where Ralph was, but it miraculously doesn't harm him or compromise his base of operations. Before this Zimforths also hurts him directly for his insolence. You can't hallucinate that level of pain. The lists he is given also contain info about complete strangers that Ralph has no way of knowing unless it was given to him by some omniscient entity.

Chances are he is real. In Space Warlord Organ Trading Simulator he a dark emperor. god of spiders, and enemy of all life. Theres two endings with him. One where he he is controlled and used as a weapon by his cult to gain power and one where he basically exterminates all life and brings ruin.

We're given a taste of M. Night Shalaman's Knock at the Door in this game. That's for sure.