I would say yes, just a very short-lived one. I'd struggle to come up with a definition of an empire that excluded Nazi Germany short of just arbitrarily imposing a minimum required lifespan. It was definitely a large, powerful, expansionist state that conquered other areas in order to subjugate them for the benefit of a metropole. The Reichskommisariats were basically intended as colonial administrations, not to mention client states like Slovakia

parts of Europe

Quite big parts