My 1e fu is weak. Not sure what an Einheriar is.
The 'glorious dead' - warriors who have died in service to the deity. 1e Hextor had nothing to do with devils, his home plane was/is Acheron. And his followers would not be eternally tortured; they would battle forever on Acheron's plains, ever-reincarnating to fight again, just like the einheriar of Valhalla.
Presumably Hextor priests present this as a glorious and much-desired fate.
There does seem to be a particular problem with 3e; Evil = Fiendish = Diabolic. Earlier editions were, dare I say it, rather more sophisticated. I'm currently running a C&C Greyhawk campaign based on the 1983 boxed set, so I've been giving thought to the role of the gods. I'm looking at something more like real world polytheism, where all the Oerdi deities would be worshipped in Oerdi nations, regardless of nominal alignment. Temples of War would have Hextor, Heironeus and Stern Alia (their mother) all worshipped together; just as the Greeks included Ares as a legitimate though unfavoured deity.