How does one detect if the player is either a vampire or werewolf?
Oblivion's old GetPCVampire no longer exists.

As far as I'm aware when you become a werewolf/vampire your race is changed. So I guess it would be getRace() if that exists.

A werewolf's race only changes when they are in beast form. To detect whether the player is a werewolf regardless of form, use the global variable PlayerIsWerewolf (and there is also PlayerIsVampire).