Hmmm very interesting.
Ok, so your're saying they ARE angels and devils? Not 'beings of superior science', but actual 'metaphysical, archetypical beings from high (and lower) planes of existance?
Ok, from what I've read about angels, in traditional Hebrew scripture, they are actually 'watchers'; it's their job to watch and chronicle man's deeds (and misdeeds) for Jehovha. That's why they do things like go incognito to Sodom and Gamorah and visit mangers in Bethlehelm.
Fallen angels, aka devils, tended to be those angels that either abandoned their charges or got to involved (mating with humans, for example). Oh, and siding with Lucipher against God.
So, perhaps all the death and dying of the Dominion war had drawn their attention. Perhaps the Devils see an opportunity to create death on such a grand scale as to punish 'the higher powers' for their dismissal.
Also, thinking of the interphase/cloaking experiment. Ever see Event Horizon? Where an experiment in space folding sends a ship 'someplace warmer'? Maybe the devils were freed from their eternal prison, and offered (or just forced) a deal upon the Hawks: We will make you the most powerful force in all creation. Simply serve us. (and, being rational Fed members, sure that these beings were something they COULD decieve (a Q, Trelene or Caretaker), took them up on the bargin.
In that eventuality, the angels are simply doing damage control; God loves free will, and if we silly humans throw in with the Damned, then we reap what we sow (or, is there a divine hand sweeping forth?).
The apocalypse, Star Trek style!
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"Yes, it's the Apocalypse alright. I always thought I'd have a hand in it"
Professor Farnsworth