- Contact with the "skin" (surface) or the "flesh" (soil) of Mother Earth in Greek myth is generally an explanation for spontaneous life, all the major characters in both these stories being literal descendants of Gaia, the Earth. The first Earth-born ancestors would have arisen from the Earth's womb in a similar manner1 to that in which Deucalion and Pyrrha's "Stone-People" and Cadmus's Spartoi do.
Cf. also how Gaia's son the Libyan giant Antaeus draws life (by way of strength and energy to revive himself) through bodily contact with his mother's surface.
- Zeus has indirectly pitted himself against both parties.
Deucalion and Pyrrha should not have survived the Flood, which was sent by Zeus in order to wipe out the human race, but on account of secret information disseminated to Deucalion by his father the Titan Prometheus, Pyrrha and her husband are able to make the necessary preparations for the oncoming cataclysm and thus live through the disaster.
Cadmus might perhaps have become a king of the Canaanites if Zeus hadn't abducted his sister Europa, which thus thrust him into a mission to retrieve her, and which is the ultimate reason for his having ended up at the site of Thebes, slaying a dragon.
Zeus's actions against both families are thus an indirect cause of the rise of both the "Stone-People" and the Theban Spartoi.
- Both are stories about the Earth being repopulated not too long after the Flood. In Deucalion and Pyrrha's case it is immediately afterwards. Cadmus is later but not by far, relatively speaking. His grandmother Libya, whom he is likely to have known, might have lived through the Flood, as it came during the reign of her father Epaphus over Egypt. Amphictyon, son of Deucalion and Pyrrha, was king of Athens at the time that Cadmus was building Thebes.
Also Cadmus and the army of Egyptian Canaanites which he brought with him to Boeotia are said by Pausanias to have fought against and driven out the children of Deucalion and Pyrrha's cousin Hyas, a tribe called the Hyantes, from the site of Thebes.
More in particular than the whole Earth, both the cities inhabited by the Stone-People and the Spartoi had existed in different configuration before the Flood, and both of the parties of the main question became royal rulers of these cities once they had [re]built them. Deucalion and Pyrrha became king and queen of Phthia in Thessaly while Cadmus became king of Cadmeia, which later was expanded into Thebes but before was called Ogygia.
- Both parties are instructed to perform apparently strange actions by the oracle at Delphi.
In Deucalion and Pyrrha's case, this is before the time that Apollo has become the patron of the Delphi shrine, and the deity who gives the couple the instruction to "cast the bones of your Great Mother over your shoulders" is their own grandmother the Titaness Themis. (Or at least so it is in Ovid's Metamorphoses.)
Later on Cadmus will be told to stop searching for his missing sister and instead follow a cow to the site of the place in which he will build Cadmeia. Like with the casting of the Great Mother's bones, the instructions to Cadmus to sow the dragon's teeth come from a goddess; in this instance it is Athena.
1. Deucalion and Pyrrha are grandchildren of the Titans Iapetus and Themis while Cadmus is a great-grandson of the Titans Cronus and Rhea, all these Titans being children of Gaia.