Cutting off the head and freezing it is nothing to do with resuscitation as the subject is already dead.
Obviously it's to make sure the subject is really dead and also security if subject was really a werewolf / vampire / zombie etc that would have shortly run amoke.
It also ensures that fresh frozen brains can be sold at huge profit if there is a shortage. Like if there is a successful zombie apocalypse.
As a side note, why Zombies at Halloween. No connection to Celtic Samhain or Christian All Saints.
Vampires do have a slight Celtic connection (see where Bram Stoker is from and also "lennan shee" is female (fairy) Celtic vampire with human lover, hence the two earlier Victorian books than Dracula had female vampires. One was Lilith. I forget the other.