but then the MC smelled of vampire due to the thrall bond. the answer to how the zombie distinguishes MC now is pivotal to establish if a zombie girl would pass the harkness test.
Not sure what one thing has to do with the other.
The Zombie guard was most likely created for the single purpose that he'll lower the bridge and open the gate for the MC.
The MC was not "smelling" any different when he was a Thrall, as any other Character would have had to comment on that.
Sneak attack you said,i dont believe the succubi daughter would step on Caleah domain,and if i remember well,you still need to beat up him for to get the chance,i think she only gets the chance by herself if you let her be raped
She is literally bound to him with a chain, so it takes the MC and Gabriel weakening the Orc and distracting him before Caleah gets the chance to finish him off on her own.
Personally I don't think you can add any combat values to the NPCs (which you can team up with), as Caleah was just a normal villager... not even a hunter let alone a soldier.
Aside of Brute, Shakalah and Gabriel none of the NPCs received any combat training.
Some have natural abilities which makes them stronger than avarage villagers, but they are pushovers in a real combat situation