This is the first thing written in the rules:
"All National Homebrew Competition entries must be homebrewed beer, mead, and cider. “Homebrewed” means that entrants cannot use professional ingredients, equipment, or other means provided by professional brewers or breweries."
Other than that, as long as they are an AHA member.... they are basically good. So, a person can "work in a brewery" as long as the beer they are entering is brewed at home and not being produced with material, equipment, ingredients, etc. from the brewery.... they are good. At least that is the way I have always understood it.
And, here are the rest of the official requirements:
Homebrewers must meet each of the following conditions as of midnight on February 5, 2017:
1. You must be a current American Homebrewers Association (AHA) member when entering the competition.
2. You must know your member number and email address associated with your membership.
3. You must be subscribed to receive emails from the National Homebrew Competition. If you are unsure, please see the FAQ page or contact Member Services at firstname.lastname@example.org for assistance.
4. No employee of the Brewers Association may enter."