Speaking as someone who is writing in a shared universe (Battletech), my characters are part of the universe and can be used by other writers, just as I have used canon charcters in my own stories. Once my stories are published, my characters stop boing my exclusively and become part of the Battletech universe. I however, would ask an author if I could use their character, to be polite. I would expect any other suthor would return the favor and ask me before they used one of my characters.
That being said, I use someone else's characters sparingly, where I can use them in minor roles, but still have an effect on the story. Most of my characters are not movers and shakers, and are not really center to the universe....
Craig
