Armok is going to be completely disregarded in the Myth release, by the way.
Armok has always been completely disregarded. He's a myth invented by fans to justify juvenile bloodlust fantasies (and, yeah, I know a procgen Blood God named Armok appears in one of threetoe's stories).
Sorry, but that is simply not true! The game title itself is "slaves to armok: god of blood". The fans just elaborated a little bit.
If I recall correctly, the name "Armok" was actually chosen for the original "Slaves to Armok", inspired by a variable called Arm_ok. The reason Toady does not include him in the myth/deity stuff is because each world is created differently in that respect. Also, Myths are just what the people think happened, not actually anything that has to be true.
I always go with the "When the world gets boring, Armok reforges it" believe. That also explains why the inhabitants of the world aren't aware of his existence (for the most part).