The man thought himself to be a messenger of God's will. The Nightmare Dream Eaters, to him, were sent from God to help pass out judgement to the infidels that would get in his way.
His brand of hatred bred fear within the gypsies and those who would not conform to his laws. Nightmare Dream Eaters essentially "eat" dreams, hope, and good, so the two were well fit with each other.
If the events of the world before it was plunged into Sleep were truly similar to what we saw in the world's dream of its final moments, I would believe that his hate of all things different could have just as easily attracted the Heartless to the world and he would have used them just as he did the Nightmare DEs.