Hmm normally the forum is pretty good in auto-bleeping. Guess thatone escaped the filter 
Yes. If you allow it once, the door is open.
PS: The only way would be, in the example above, for you to make a specific license agreement with that first person.
That involves some overhead on yiour end. lawyer work, etc.
Are you willing to spend your companies’s resources because someone wants to make a fan based game?