You know, I'd written up a post disputing that idea on the grounds that there isn't a sunken city or temple in that scene, but it turns out I'm wrong about that. I see now that there is, and even that it's associated with dolphins, as in "The Temple."
On the fifth day the sailors were nervous, but the captain apologised for their fears, saying that the ship was about to pass over the weedy walls and broken columns of a sunken city too old for memory, and that when the water was clear one could see so many moving shadows in that deep place that simple folk disliked it. He admitted, moreover, that many ships had been lost in that part of the sea; having been hailed when quite close to it, but never seen again.
That night the moon was very bright, and one could see a great way down in the water. There was so little wind that the ship could not move much, and the ocean was very calm. Looking over the rail Carter saw many fathoms deep the dome of a great temple, and in front of it an avenue of unnatural sphinxes leading to what was once a public square. Dolphins sported merrily in and out of the ruins, and porpoises revelled clumsily here and there, sometimes coming to the surface and leaping clear out of the sea. As the ship drifted on a little the floor of the ocean rose in hills, and one could clearly mark the lines of ancient climbing streets and the washed-down walls of myriad little houses.
Then the suburbs appeared, and finally a great lone building on a hill, of simpler architecture than the other structures, and in much better repair. It was dark and low and covered four sides of a square, with a tower at each corner, a paved court in the centre, and small curious round windows all over it. Probably it was of basalt, though weeds draped the greater part; and such was its lonely and impressive place on that far hill that it may have been a temple or monastery.
It certainly seems to fit the description of the Atlantean temple. There are only three arguments left against the idea that the dead sailor in the Dream-Quest
is the commander of the U-29, and all of them can perhaps be shrugged off as "Dreamlands logic": one, that there's no mention of any laurel-crowned youths (fairly unimportant, as the rest of the description of the city and temple match up so well with that in "The Temple"); two, that the sailor in question is not wearing a deep-sea diving suit but "the silk robes of Oriab"; and three, that the city in question isn't as deep as the Atlantis described in "The Temple," being visible from the surface, and close enough that Carter could make out details like what kind of robes the man was wearing and the fact that he had no eyes.