I would assume most old-style vampires tend to avoid having fire or light mages as slaves. It's a bad idea to severely mistreat someone you have a mortal weakness to, after all. I wonder which elements vampires are most resistant to...

My guess is that it depends on the family, and I would also guess that some older families have had extremely bad experiences trying to split up mage families. Like poor cousin Martha, who was given a bird's eye view of the landscape after upsetting the air mage servant. Granted, the servant was executed, but I don't think they cared much.