How does an SMPS initialize?
before posing my question, I would like to make the assumption that
  all the electronic circuitry in an SMPS is DC powered by the SMPS’s DC
  output itself


An SMPS uses quite often a tertiary winding to obtain power for itself. The initial switching must have begun for this to work though so there is a bleed resistor from the raw dc that provides power at start up: -



Note the tertiary winding and the resistor feeding pin "V".

Very low power devices steal a bit of power down the fly-back back-emf protection devices or through the primary winding.