Or at least an expy of Batman. Okay, let's face it, they're both detectives who witnessed the brutal murder of their parents at a young age.
A very disconcerting fact is that the opium-induced experience of Harvey in Hotel plays out exactly as the encounter between Dale and Mr. Crow in Paradox, when Crow gives Dale the knife. And the phrase "you know what to do" seems more apt in the context of Paradox. So it seems not totally absurd that Harvey in Hotel was in fact directly experiencing what Dale would have years later in Paradox - as if (s)he were him -; from that it can be presumed there must be some profound relationship between Harvey and Dale.
Moreover, Harvey is a civilized animal during Hotel, and in fact every other such creature in the game, with the exclusion of Mr. Bat, is in this form after interacting with the elixir (Crow) or its components (the Eilanders, assuming they're Owl and the guests); that gives credence to the theory that Harvey did either drink the elixir, or partecipated in the rituals of Paradise.
The ultimate clue is the fact that Mr. Rabbit killed Dale's family in order to obtain the substance of his past lives: that doesn't really makes too much sense unless we assume that Rabbit is a reincarnated Eilander (presumably the soul of the Mr. Rabbit eaten in Hotel), and that Dale is in some way a descendant of the Eilanders - though presumably not by a purely paternal line since he has a different surname.
A theory that fits all this is so thus: Harvey was the first son of Jacob's mother, and he was sacrificed before Jakob could remember of having a brother - and she wasn't able to stop the sacrifice; Harvey still managed to impregnate someone before being sacrificed. I wouldn't exclude that the mother began her researches specifically as a way of reviving her first son, and she actually succeeded in a way after the events of Paradise. Harvey's son/daughter would initiate a blood line ending in Dale.Also note that this would explain why the guests' souls were so aggressive toward Harvey after being freed from the tanks in the room of Mr. Owl, other than him(or her?) having just killed 'em
