Cartoons that make fun of hitler generally make it obvious that hero is a good person and hitler is a bad person. That doesn't work in hazbin where you have cannibals and rapists treated as quirky tumblr sexymen living in a wacky edgy isekai. Mocking hitler would feel insincere.
Vivzie also put Dahmer as a handsome cannibal chef in hell and that's why this so many people headcanon other serial killers and monsters as celebrities in hell. If we went by her own "world building", Hitler would HAVE to be a celebrity/overlord due to sheer infamy alone (and a twink sexyman too).