[Keeper of Dol Guldur]

I've made the comparison before, between Sauron and Morgoth. But the Mouth of Sauron is to Sauron what Sauron was to Morgoth. A commander of a fortress and sorceror, but hardly the military power. That means the Nazgul are to Sauron what the Balrogs were to Morgoth, of course, after seeing that some of the Balrogs ran like girls after the great wars, Sauron decided to bend his team of terrors to his will. As for the Mouth of Sauron, much like Sauron himself was once, he is favored because he has an ambitious mind of his own, and his own aims, all capable of being done under his master's rule.

The Mouth of Sauron certainly had plans, he figured he'd sidle into control of all the West and take up abode in Isengard, and maybe even deal with Saruman himself for his master.

Only those beings who respect and fear Sauron never referred to him by name, and since most of his tools did both. But someone like the Mouth, with no respect for anyone after his ages of life at the top, wouldn't have a problem with it, just like Saruman didn't have a problem with it.

Maybe the Silm can be linked to the LOTR in a sort of 'History repeats itself' sort of thing. Who prepared Angband for Morgoth's return? Sauron. So who prepared and directed the reconstruction of Barad Dur? The Mouth of Sauron.

Just some thoughs.