The person charges around 50 gold per every 1:00 minutes, yes it's good if you need help fighting.
He doesn't steal anything but henchmen aren't always the most strong.
Also you can sacrifice henchmen in the Chapel of Skorm which is located in Darkwood Camp for Evil points and Skorm's Bow, the most powerful bow in the game.
As for the ghost...
Next time you have a question regarding Fable or Fable: TLC you should post it in the
Fable Help section.