I think it takes a really big name to genre-jump successfully, and even then, I'm not sure it's necessarily all the readers following the author as the author using name recognition to pick up new readers in new categories.
When Stephen King published Different Seasons, he was already famous. Horror fans I know sometimes bought DS but often didn't finish it. I also know people who read it that didn't read King's horror. I don't know if this small sampling is typical, but it suggests a possible pattern.
Ten years after Stephen Chbosky did Perks of Being a Wallflower, a bestseller that became a movie, he released Imaginary Friend. Unlike the teenage characters in Perks, the main character here is a little kid, though other characters are townspeople of all ages. Also unlike Perks, which is usually considered literary fiction, Imaginary Friend is hardcore horror that reads more like Stephen King or Clive Barker wrote it than like Chbosky did. Though it wasn't as successful as Perks, it was a bestseller. Both books are four-star on Amazon, though Perks has more than 50,000 reviews, and IF has just a little over 4,000. So the genre-jump worked, but something along the lines of Perks might have done better.