Of note while surfing the Assembly-CSharp.dll file for new additions, seems like there is a Man character class, and in the character folder, a Man character with Slave assigned. Haven't played much (been busy), so can't confirm if they are capturable as of yet. They also don't have any sex animations listed.
Having a quick poke through myself, there's a few other things I have noticed that might be relevant for future updates.
The nation file that determines how we get attacked is also referred to as the human nation in the file itself, so it might be the case that we only get other races attacking us if we venture beyond the human kingdom and interact with other races deliberately. Maybe even some kind of diplomacy system is on the cards for the future? Duplicating the file and changing the names to try to add another nation doesn't seem to do anything yet though.
There's art assets for a sister settlement that is unused. I'd guess that it was originally intended that one human settlement was to be normal warriors and the other one be for sisters, but it was decided to just make them both normal warrior camps near release?
There's still standing and milking animations for multiple pregnancies, even for the new Oni, but they are still missing animations for multiples during sex.
There's still remnants of elf ears for the normal women in the art files, but they are not present in the newer assets for sex with orcs, so I'd guess that having multiple races operate on the same template has been shelved and it was just a remnant of early development. More curiously, the human men still have a race=0 tag, while race=1 is what enabled the half-finished elves for the women.
Colour code 6 is used for orcs and onis, but I haven't tested to see what it actually corresponds to. Maybe teeth?
The Orc has a skilldamagemultiplier of 100%, which is at odds with the tooltip that says it does 150% damage on the jump attack. Has anyone tested this to see if it works properly?
Relating to above, many character-specific stats have been shifted from base values onto multipliers. This actually fixes one notable issue I had with monster balance before; in particular, how to balance the flat increases to a monster's stats with balancing monsters around their base stats. Onis having 200% damage on their attack skill means that they outscale goblins for damage by breeding as they'll always deal double the damage of a similarly-bred goblin, although it remains to be seen whether they are worth the 3 deployment points.
They'd be mostly useless and probably buggy as hell (the slave deploy doesn't check genders, so male pregnancy is technically possible, but they likely couldn't give birth), but possible.
The Slave deployment bit doesn't check for male vs female, but the conceive function does check to see if they are female. No Mpreg is a hardcoded feature.
Maybe it's possible that eventually we will see male children from player+slave? They could then either be pressed into combat, or possibly exist as some kind of non-breeding slave for some other function around the burrow or simply sold.
The men do also have portraits though, so I guess that's another implication they might eventually end up being capturable? Unless the devs have some plan for humanoid portraits appearing elsewhere, such as a diplomacy system or visiting traders...