I always find that funny, considering it was almost certainly by accident and they'd probably try to grimdarkify it more if they realized. They do the shit they did to the Tau on them.
i remember the insane crying by all the fans being so utterly distraught over the existence of "Good Guys" in their grimdark setting, also all the standard asian hate that happens less now, because anime is more mainstream
But it'd be just like a disciple of Metamorphosis to feign fealty to the Lord of Pleasure while still carrying out the aims of the Lord of Change as subterfuge. For all we know, it could be a ruse specifically to flummox OP, and they'd never know.
Just as long as they aren't secretly worshiping the corpse emperor they should be ok. Too many chaos worshippers get hung up on impurity tests and being "the right kind of chaos" when we really need to be presenting a united front against the followers of the corpse emperor. Chaos unity is important, we all want a galaxy free of the imperium for the glory of our dark gods, and if we spend all our time arguing amongst ourselves that can only serve the corpse on terra
Chaos Undivided Thought is the best path forward, and you don't want to fall to revisionists that say Abbadon should have focused on building Chaos in the Eye of Terror before spreading it to the rest of the galaxy, but you shouldn't disregard those sympathetic to our cause just because they are more dedicated to perfecting their murder-symphony than they are spreading Papa Nurgle's gifts
Look, they sold me on the concept when they gave me an electric guitar and amplifier that literally bursts eardrums and melts faces. Chaos Noise forever.