It’s been a while, but I’m pretty sure Dath’Remar’s faction knew exactly what Azshara was up to. He and his followers were among the Highborne who’d summoned in the demons on her behalf, and they remained loyal even after the initial night elf massacre. He joined the night elf resistance chiefly because the Highborne had nothing to show for their toil, Sargeras’s promises were beginning to ring hollow, and the demons butchered a bunch of his brethren to punish their lack of progress.
… it’s like an elven precursor to the last two Horde rebellions.