Leader of the pack won't bite :S

[Sleepycat]

they may have fixed it *shrugs* 

I've never let my sims make any servos so I've never tried it but I do know for a fact that it was possible. My daughter quite enjoyed having male servos knock up the female sims    not really worth doing IMO since the baby will always be a sim and not a servo (although I think the father did show up correctly as a servo in the family tree)

[Gwill]

How do you make a Servo a Zombie?

Same way as any other zombie, you just kill it an ressurect it.  Servos can die from fire, satelites and cow plants.  Might be other ways, but those are the ways I've found witout cheating.  Cow Plant is by far the easiest.