The Anu incubated a slave race with paired down genetics so they could never rise up and rebel. They did not necessarily splice their DNA with "inferior" beings- because what these ancient scribes who wrote the clay tablets would never be made aware of was the fact that the original humans on earth were actually MORE advanced than the Anu and were in fact living in other parts of the planet.
Still, I feel Sitchin's work is resourceful and very interesting and scholarly.