Bumping because that was posted rather late. With some content ideas so that it doesn't seem like a waste of a post.
The Angels and Demons now living among the human world can be distinguished by sight but one of the least advertised but most notable distinctions is that Angels and Demons, as a rule, have no genitalia. It makes sense in context, the vast majority of Angels were created by God for a specific purpose while most Demons were either Fallen Angels or being similarly created by the Devil for a specific purpose. They may look kind of like men and women but they don't actually reproduce sexually, so they don't have the equipment to do so.
There is are a few known exceptions to this rule though. For the demons there were the Incubi and the Succubi, demons that specialized in sex-related sins. For the Angels there were the Angels of Joy, a faction of God's choir led by the female Archangel Haniel. An Incubus is always Male, a Succubus is always Female, and an Angel of Joy can be either gender. It is rumored that particularly powerful members of either type could switch genders at will, but ever since the Curb Stomp War this ability was lost.
Which leads to the question of half-breeds. In short, yes - if they have the biology naturally it works. Incubi and male Angels of Joy can and according to their respective factions have in the past impregnated human women while Succubi and female Angels of Joy have become pregnant by human lovers before. Both sides forbid the practice, granted, but it could be done. The offspring of an Incubus and a human woman is called a Cambion, the offspring of a Succubus with a human man is known as an Alu-Fiend, and the offspring of a either gender of a human and either gender of an Angel of Joy is called a Nephilim. This leads to the question of what happens when an Incubus or Succubus has offspring with an Angel of Joy. The honest answer is nobody knows, both sides were not only expressly forbidden from such a thing but were told that their body fluids explode when mixed - but the Curb Stomp War proved that wrong.
Its also worth nothing that while both sides forbid the practice of breeding Cambion, Alu-Fiends, and Nephilim the effectiveness of the bans varied. Nephilim haven't walked the Earth since the Bronze Age, the last being that was even rumored Alu-Fiend died from Bubonic Plague back in Medieval Times with the last confirmed Alu-Fiend being even further back. Cambion though, get snuck in once in a while - the surviving demons are pretty sure Jack the Ripper was a Cambion though they can't prove it or point to who was the father.
This was thought to be a moot point either way as for a while there were no known surviving Incubi, Succubi, or Angels of Joy. However, this has change in recent months. First in Italy one of the relocated Angels decided to try her hand at fashion design. "Halo" as she became to be known actually turned out to be a natural at it. A success story for the angel/demon relocation program, a rumored sex scandal circulating in the tabloids led her to confess that she was an Angel of Joy and as such she really was biologically female. Fortunately, the world of fashion seemed to love her all the more for it. Rumors still persist that she's had more lovers then she lets on, one or two even claiming she's not just an Angel of Joy but the Archangel Haniel herself - but these are mostly just rumors.
What really opened these questions back up was "Confessions of a Horny Devil", a blog recently started by "Nick Brooklyn". A relocated demon who has done a better then average job at modernizing, he's gotten work as a contracted Author/Writer who does a good enough job to make a living and survive in New York. In the blog however he's recently "outed" himself as not just a demon but an Incubus that didn't just look male but really is biologically male. So now it's pretty much considered just a matter of time before more Cambion and Nephilim start popping up. Sure, "Halo" says she's on birth control but she and Nick are rumored to not age so it's just a matter of time.
"Confessions of a Horny Devil"
A recent hit on the internet that's gone viral, the world for now seems to get a kick out of the idea that one of the relocated demons has figured out the internet enough to start a writing career. The blog's popularity is nothing short of viral and book deals based on it are already rumored, if its frowned upon in polite society. The fact that in the first entry he outs himself as not just a demon but an Incubus that really is biologically male adds to the appeal. The blog is frowned on by assorted groups and polite society of course, but that doesn't stop people from reading it.
Indeed, he seems to be in a "no publicity is bad publicity" phase where as long as he's not too evil the readers root for him all the more. For example, he's recently started going to Sex Addicts Anonymous meetings to pick up new sexual partners and write about them in the blog. (At least that's what the blog claims, the truth is that while he's not really planning on giving it up he really is considering taking it down a notch to work in with society better.)
Of course, with the increased fame and the book deals comes more attention he doesn't like either. And he may not age or get sick, but he can definitely still die. And ever since Lucifer got fried he's powers aren't dead but they're nowhere near as dramatic as they used to be.