Following just fwiw.
"Hierogrammate" seems like an odd title for a being which purports to be in charge of the universe or whatever Tzadkiel's claim is. The Greek is hierogrammateus/plural hierogrammateis. It means "holy scribe" and seems to have been used most commonly as the Greek term for a class of mid-high ranking Egyptian priests, staffers of the "House of Life". I guess Thotmatkef (sp?) in SoS would have been called a hierogrammateus in Greek. Part of the elite but not the top rung, for which a different term was used.
(In Greek cults it seems not to have been such a high status thing: any job title within a cult or temple bureaucracy could take the "hiero-" prefix, it seems, and "hierogrammate" doesn't appear to have necessarily meant much more than "temple clerk", in the same way that there was sometimes a "holy debt collector". I would guess that Wolfe was thinking of the Egyptian context, to the extent the titles are supposed to have any connection with the historical usage.)
The common term for priest was hiereus/plural hiereis. (For both job titles, the "-eus" as like in "Zeus"). I suppose that this is where Wolfe's term "hieros" comes from. It was also apparently a term early Christians used for themselves.
"Hierarch" was the term for a cult official responsible for
overseeeing execution of ritual practices and so on.
I get a picture of an organization with hieros (now disappeared) at the board level, so to speak; hierogrammates as senior execs; hierarchs as middle management and hierodules as the blue collars.