Good analysis, SorO.
Regardless of its ECL, a monster with class levels uses the base attack bonus and base save bonus progressions of its class (rather than the [epic] progression shown on table 1-1) until it has 20 character levels. Beginning with its 21st character level, it uses the progressions shown on table 1-1.
In any other place where "character level" is indicated, you can use effective character level instead. For example, a creature with a level adjustment of +5 who is also a 13th-level fighter/3rd-level blackguard is ECL 21 and eligible to select an epic feat provided he meets the prerequisites.
So this is what should be happening. The only other
direct (well pretty damn direct) contradiction to this seems to be the Dragon prestige classes in
Draconomicon. Most all of them can't be taken until after 20 HD, and they all, IIRC, grant full BAB. The Bloodscaled Fury requires BAB of +22, and grants full BAB for all its 12 levels.
That gives some precedence for dragons to just flat out ignore the epic progression rules on BAB and saves, but maybe that should only apply to the PrC's in Draconomicon...
Maybe I should just fudge the rules in a way to try and make sense of things like the Frost Giant Jarl and the advanced Eldritch Giant... maybe it takes 20
class levels before Epic BAB/saves go into effect. I know this directly contradicts what the ELH says, but it seems to be the best middle ground between "racial HD don't follow epic rules," "human classed characters follow epic rules," and what is presented by things like the Frost Giant Jarl and the Dragon PrC's in
Draconomicon.