Lots of theological discussion, and I was in Russia for a month and could not be involved!
One thing briefly on the Satan-Herod business: There are four important Herods in the NT:
Herod the Great, who tried to kill the baby Jesus.
Herod who killed John the Forerunner (being tricked/seduced to it by his evil second wife -- a Wolfean touch!), and who mocked Jesus.
The Herod who killed James the Apostle and imprisoned Peter, and who was killed by an angel (messenger) after posing as a god. (Acts 12 -- and this may be closest to the Severian material -- the murderous Typhon imprisoning Sev and then being slain by him).
Herod Agrippa, who was "almost persuaded to become a Christian" by St. Paul.
Since Wolfe's books are thematic and not strictly allegorical, any "Herodian" theme could easily see Herod as a stand-in or agent of Satan, in terms of Herods 1 & 3 above, and partly Herod 2 also. Typhon can be "like" Satan and "like" the Herods without being too closely identified with either, in some allegorical manner.
FWIW, at this late date.
Nutria