Whatever we think may think of the possibility or likelihood that fallen angels and humans may have bred offspring or not is unrelated to what may have actually happened.
For humans to frame the question of what is possible based on what humans may think or have proved in their current level of scientific understanding is sufficiently anthropocentric to be considered empirically silly.
However, that said, I am not saying I agree with the following but here it is...
DNA studies indicate that Humans and chimpanzees carried on interbreeding for thousands, perhaps millions of years after the two species diverged.The researchers say human evolution seems to have been much more complex than previously thought. This exchanging of genes probably helped both species survive more successfully in their environments.
Team member, Prof. D Reich says that this is just a hypothesis as it has not yet been proved. However, he said it would explain multiple features of their data. Their hypothesis is that there was an exchange of genes between our human ancestors and chimpanzees after the two species diverged.
This study was carried out at the Harvard Medical School and the Broad Institute of MIT and Harvard. You can read about the study in the journal Nature.
Chimpanzee DNA sequences are the most similar to humans in the animal kingdom. After divergence, the differences took place as a result of tiny mutations over time. If scientists can pinpoint these differences in human's and chimp's genomes, it is possible to map out a history of each species' evolution.
Source: MedicalNewsToday.com
I don't see any genetic similarities between chimps and fallen spirit beings. It would more akin to trying to mate with an amoeba. It won’t be much fun and it will only anger the amoeba.