A vampire servant is someone who has been bitten by vampire and made into a loyal protector. They are not made into full vampires, but they have great strength and seem to survive nearly everything a vampire can. They can survive in the sunlight like an ordinary person.
While there is a clear distinction between vampires and the more-than-human ghouls that serve them it could be said that the vampires that are recently turned by older, more powerful ones like Jerry or Regine Dandridge are beholden to them. This master/ disciple relationship makes the younger vampires the thralls of their master's will much like the ghouls Billy Cole and Bozworth.