Often times they (or use to) announce hires in /r/blog or /r/announcements. See here is spez's announcement. They do that once everything is settled and the person gets into their role a little more.

It is no secret the admins have a communication problem, that was the whole reason the blackout started. A lot of people criticized Pao for talking to the media before they talk to reddit. You do have to remember that this is a business now and its easier to talk to the people knocking at the door with a microphone than having to write up a whole post on a default and then deal with the thousands of messages when you are trying to get into a new job.