[Boromir88]

Some more ideas...

Originally Posted by Form

I think there's a tendency to think of Mordor as a secretive society, partly because we know so little about it and partly because to the good guys the Ring (and what they're doing with it) is a great and terrible secret, but we don't actually know what is secret and what is public in Mordor. In a "panopticon" sort of way, I wonder if things might have been more dreadfully public than we think.

Quite true. It's possible Gollum once having something important to Sauron for the War, captured and "escape" was common gossip among the rank and file in Mordor. Grishnakh sounded like he knew more than Gorbag, or Shagrat, simply because he was more intelligent. As quoted by Inzil, he refers to himself as a "messenger" - granted a "trusted messenger" but a messenger doesn't necessarily denote someone of high rank or importance. (Then again, the Mouth of Sauron is a messenger)

Some facts we do know for sure though. When Grishnakh slipped away after the fight with the Isengarders, it was to meet the Nazgul he previously said was waiting on the east bank. And presumably he informed the Nazgul that Saruman ordered his orcs to take the prisoners to Isengard. Grishnakh later rejoins Ugluk's group:

"So you've come back?" he [Ugluk] said. "Thought better of it, eh?"
"I've returned to see that Orders are carried out and the prisoners safe," answered Grishnakh.~The Uruk-hai

This is an assumption, but I think a fair one to make based on how the events in the chapter play out, Grishnakh was ordered by the Nazgul something along the lines of...the hobbits have something important to Sauron, or have important information about its whereabouts, this can't fall into Saruman's posession, get the hobbits and bring them back here to be taken to Mordor.

Perhaps Grishnakh even knew it was a ring, if he was also involved/knew more info about Gollum's torture. Initially that made me wonder, why would an orc be trusted to know specific details (details that I don't think Gorbag and Shagrat knew)? But putting on my Nazgul cloak, it would be much better for Grishnakh to get the ring (if one of the hobbits had it) than for Saruman to get it. Because if Grishnakh got it, he either proves to be the "trusted messenger" and returns with it/or the prisoners. If he's untrustworthy, Grishnakh is far easier to be dealt with than Saruman, who Sauron (and his agents) already know to be untrustworthy.

We might not know the extent of how tightly closed Sauron keeps the lid in Mordor. But we do know he promises rewards for showing loyalty to him and proving one's worth. They might be empty promises, and deceitful, but he uses both rewards and threats to get what he wants:

"But they shall help to rebuild Isengard which they have wantonly destroyed, and that shall be Sauron's, and there his lieutenant shall dwell: not Saruman, but one more worthy of trust."
Looking in the Messenger's eyes they read his thought. He was to be that lieutenant, and gather all that remained of the West under his sway; he would be their tyrant and they his slaves.~The Black Gate Opens

That Nazgul, most likely would do the same with ambitious orcs working under them. When Grishnakh tells Ugluk about the Nazgul, to me he sounds envious. He's "shivering and licking his lips" "savored painfully," and says Ugluk ought to know "they are the apple of the Great Eye." As if he was promised a reward to make sure the hobbits did not go to Saruman.