I wouldn't be so quick to that, especially considering Orlando (Diagon) and Osaka (Hogsmeade, and they even had the Death Eaters for a year) have gotten away with Potter being fully present during their Halloween events.
Might Nintendo be extremely strict on how Halloween is celebrated within the land (More-so than WB/Joe for when Osaka began to put up decorations for their Hogsmeade during the time)? Sure, but I don't necessarily discount it from ever popping up with HHN. It also somewhat..blends with the Target Demographic, even if most are there for the horror.