Agreed, but there is a difference between not hiring someone because of their opinions, and telling them "you represent us now, don't say anything stupid please, ok?"
("oh, and here's the script for the next show with a bunch of stupid things we'd like you to say")
People represent an agency while on official business for that employer/egency. The employer/agency does not own that persons personal lives and as such should stay out of it as long as their personal life is not illegal and/or does not affect their performance.
In this case one could argue (I would) that the article was him acting as a Duck Dynasty rep since being popular is why he was interviewed.