can you create an offspring from ancient human's DNA?
A species is generally defined as a group of organisms that can breed and produce fertile offspring. So, if you are extracting DNA from the an ancient human that is indeed the same species as us (homo sapiens), then by definition, you will be able to combine it with modern human DNA and generate offspring.

This is just stating the theory, the actual biology behind extracting that DNA and using it to fertilize offspring will be... messy.