Here are the relevant references from the Books where Nipples are mentioned.
I make no pronouncements on these matters, but report them as I find them.
Arrive at your own conclusions.
I wish you well,
Even in the flickering light I could see the beautiful mottlings on her body, on the sides of her breasts and body, red and white, still rich and subtle in her hot, blood-charged skin. The chain dangled to the floor, where it lay, half coiled near the ring. The fruit of her body hung free, and lovely. The nipples were still arch.
I touched the nipples. How beautiful they were, large, delicate, sensitive now, almost painfully swollen with blood. I kissed them.
As a Gorean master, curious, I gently, delicately, touched her nipples. They were sweet and high, full and blood-charged. I was pleased. I kissed them, gently. Her responses were not feigned.
I crouched beside Melpomene. She lay on her back, on the love furs. She was panting; her nipples were delicately rigid; her skin, from the dilation of capillaries, was a patchwork of red and white.
"Do you think such things cannot be told from your breathing, the mottling of your skin, the condition of your nipples, the timbre of your voice?"
Her skin was mottled deeply with red blotches. Her nipples were in lovely erection.
"Certain things their bodies cannot dissemble," I said. I took the girl by the hair and, gently but firmly, pulled back her head. "Do you see these discolorations," I asked, indicating irregular reddish splotches on her fair skin, "the results of capillary distention?"
"Yes," he said.
"They are correlated with her pleasure."
"Interesting," said Cuwignaka.
I then turned the girl in profile to him. "Consider her nipples," I said. "They are hard and high, distended, sweet and swollen with blood."
"Yes," said Cuwignaka.
"This sign, too," I said, "invariably indicates the presence of sexual pleasure in the human female."
"Come around to the side of the table and kneel here," he said. I did so. He then bent over and, cupping his left hand under my left breast, held it steady and, with a grease pencil, across it, above the nipple, inscribed four characters. "That is your mill number, Tiffany," he said, "four thousand and seventy-three."
Another fellow was thrusting up the fringe dangling from the narrow, twisted strip of cloth, covered with sequins, which was bound about her breasts, this serving to conceal her nipples.
Rowena and Lady Telitsia, breathing heavily, their nipples erected, their bodies red with usage, bruises on their arms where they had been held down and roughly handled, turned to their sides and, palms on the tiles, looked up to the stage.
I had known about the other sorts of things. They had been graphically illustrated to us in the house of my training. Some had to do with skin blotching and nipple erection.
"Your nipples," he said, "are swollen. Your skin is like a field of scarlet dinas."
A fellow there swiftly leapt up from a naked woman, one with richly blotched skin and helplessly erected nipples.
Her body was covered with red blotches, from the recent racing of her blood, the excited distention of thousands of capillaries. Her lovely nipples were not yet subsident.
"Your skin is blotchy," I said to Phoebe.
She laughed, ruefully. "Yes, Master," she said. The new slave, her head down, smiled.
"Remove the garment," I said to her. "Replace it in the chest. Then resume your position here, beside me, on all fours."
"Yes, Master," she said.
I then again, in a bit, regarded her. No longer was she in the dignity of a garment. Her breasts, in her present position, that which I had dictated, were beautifully pendant.
"Can you write?" I asked her.
"Yes, Master," she said.
I reached to her.
"Oh," she said, softly. "Oh!" I had taken her nipples gently, first one and then the other, between my thumb and forefinger. They, too, it seemed, had not forgotten their state of but a few moments ago.
Lavinia's nipples were still erected. They were very lovely.
"You did not respond to the man who was here?" asked Aynur.
"No!" I said.
"How then do you explain the condition of your body, when you were found?" asked Aynur.
"I may have felt, a little," I whispered.
It would do little good, I feared, to attempt to deny, to an observer as astute as Aynur, what would have been obvious. There are so many signs, the dilation of the pupils, the helplessness, the sheen of sweat, the oils, the smells, the mottling of the body, the erection of the nipples, such things.
I knelt, covering my body as I could. I was muchly flushed. I covered my breasts. I did not want them to see the erection of my nipples. I was gentle. They were tender. I kept my head down.
Her head and hair were back, hanging down. Her body was gorgeous with color, a mottled scarlet tapestry. Her nipples were tightly pointed.