What an individual performer does with their fan mail is, of course, up to them. Some trash it. Some hire a service to answer it. Some read it. Some send a form letter response. Some answer the letters individually.
JHC does get the fan mail to the performers. A number of people have posted here that they received responses to letters. I believe Jackie (or was it Emmy? I'm pretty sure it was one of the BBB) got a great response from Dave Goeltz a while back-- included answers to some unique questions.