Once the rider boards the aircraft, he will greet a flight attendant, present his credentials and tell her that he needs to see to the Captain. The rider may be questioned about the basics of his company such as what does he fly, where does he fly, his chief pilot, his two letter airline code, etc. If he dressed properly and speaks like a pilot, there will be no problems. Remember the Captain is the final authority and can refuse to take the rider. Some Captains are inquisitive, but most just don't care.
Many Captains are members of labor unions.
A worse case scenario would be a war between union and non-union people. If the aircraft is full, the rider should plan on the actual jumpseat in the cockpit. The actual Jumpseat is a third seat, which is extendible between Captain and First Officer for just such occasions as this. He should be prepared to make small talk about aviation and his company upon reaching a cruising altitude, but nothing too in depth. Only speak if spoken to when below 10,000 feet.