I've never been able to call a ghost from the tombstone alone. I can only ever do it with the book of life, and it's worked for regular Sims and vampires alike. I've sometimes had Sims mourn at a tombstone at night and the ghost happens to come out afterwards, but since I can't repeat it, I'm pretty sure it was a coincidence.
I have wondered why "Build Skill" is sometimes an option for a Sim that's not there and sometimes it isn't. I never associated it with the Sim being a vampire or not. Now I'm curious...is it based only on what your Sim was doing at the time you "left" to follow someone else in the household?