Dreams in Darkness: Opens with Batman as a patient in Arkham due to hallucinations. This is where the conversation happens with Dr. Bartholomew, which includes mention of “Jack Napier, Harvey Dent, and Pamela Isley…or as you [Batman] know them: the Joker, Two-Face, and Poison Ivy.”
Bat’s hallucinations are caused by exposure to the Scarecrow’s fear gas, which he is planning on releasing into the water supply–thus providing an inspiration for Batman Begins.
So that settles that.
It seems our friend Mr. Tetch’s name goes way back to the comics, so I’m not sure how likely it is to even uncover a definitive cite for its origin.