I do agree that they can ask him to be clean shaven. Just as they would ask him to remove any facial piercings, or have any tattoo's completely covered up if they were a problem.
I do however think its unfair for him to have to pay for the flight. By rights, if they want him to go that far from home & where the job is, they should arrange that, or have the boss come to them.

I would get him to seriously consider shaving his beard. It would be a great job to have, & not really a huge price to pay.