Yes. The idea of the souls entering through the Gates of Man in the Presapae cluster of Cancer is why they chose that sign to rise in the Thema Mundi.
Not mythology. Hellenistic philosophy, though it does tie into Hermetic philosophy with the Moon (the ruler of Cancer) being the last sphere the incoming souls pass through before being born and Saturn (the ruler of Capricorn) as the last sphere souls pass on their journey back to heaven after death. You also have to realize that Cancer and Capricorn are the Solstice signs, which have their own special meanings in solar mythology.
Mythology or philosophy, I'm not touching that with a ten foot pole.