I'm coming into this discussion late, and I may well have missed this answer somewhere listed above, but I have a question about a specific licensing scenario.
Paizo presumably owns their interpretations of mythological creatures, like the kelpie, and so the kelpie as presented in Bestiary 3 is Paizo owned material—but Bestiary 3 is published under the OGL. If I wanted to reference pieces of the kelpie statblock for my own version of a centaur ancestry, would I be forced to publish that content under the OGL, or would the Community Use or Infinite License be required? Does that content fall under the designation of Open Content or Paizo owned content, I guess is my question.
Similarly, azarketi are an ancestry invented by Paizo and have yet to be republished in any ORC licensed book; I assume any reference to them or any related ancestry feats or features would be Community Use or Infinite and couldn't exist under ORC.