I was playing a skirmish, for once, after a long while and noticed a lieutenant, Rage of Morgoth. Another example is Spawn of Angband. In the storyline, we see Antheron, who is obviously Annatar, but why this in particular? I thought the Silmarillion was off limits with lots of copyright goulash.
In the movies: Gandalf mentions Balrog of Morgoth, but refrains from using the names Palladan and Alatar.
So, what exactly are the limits to these copyrights? (Thinking in terms of movies, here)