It's striking that the remake of Nosferatu from Werner Herzog came out in the same year as Salem's Lot, 1979. It came out in October in the US, but already in January in Europe. It's possible the producers of Salem's Lot or Tobe Hooper saw it and decided to base the look of Barlow on Orlok. It just seems too much of a coincidence.
Does anyone here have the book by Tony Earnshaw about the making of Salem's Lot? Is it mentioned in that?
Okay, just read Earnshaw's book and yes, Barlow is based on Orlok. He didn't want to make this vampire the suave lover that movies were turning to. He wanted Barlow to embody evil. And he felt going back to Orlok was the way to do it. Stephen King was not happy with this.