BAe Systems is a private company but Corporate Air Travel (the section of BAe which operate the 146 and Embraer) well they have a normal AOC and operate like any other normal airline. The passengers are technically fare paying with the fare paid by employee's department. The terminal is also set up and operated to normal security standards. So shouldn't be an issue for other operators, just the logistics of operating out of a secure site which normally requires security clearance for every visitor.