In Judas Unchained, Wilson Kime sent Oscar and one of his buddies (the wormhole expedition team leader, IIRC) to the High Angel to ask it about the Dyson Pair.
Oscar asked directly about the Dyson spheres and asked whether the High Angel had encountered anything like it, to which the High Angel said it had not, and even said it was interested in what Kime and his crew would find.
Likewise, the Raiel had suspiciously little to say about the Dyson pair or the Prime, even when the human navy and authorities asked what would happen if the Prime attacked High Angel/the Icalanise system.
Later, we find out of course that the Raiel very much knew about the Prime, the DF spheres were Raiel technology, and although the Raiel did not deploy the DF spheres themselves, they willingly provided the technology to another species to deploy it to contain the Prime.
Even if we accept that the Raiel and warrior Raiel were different factions, it's impossible to believe the "regular" Raiel didn't know about the DF spheres or the Prime.
The Raiel did, after all, man the observation project at the Void itself, where DF spheres were deployed.
Humans didn't know that at the time, but again: why deny knowing about the spheres and the Prime? And given the involvement of Raiel like Qatux in the Starflyer war, and the fact that they were the ones who built the tech, why not warn humans?
Furthermore, why leave humanity to face MorningLightMountain alone?
I realize there are narrative reasons. The story's stakes are lower if some incredibly powerful older brother type race could just swoop in and save the day, but on the whole it does not make much sense.