As for the Telmori being tainted by Chaos – of course being cursed by Chaos taints you with Chaos, and of course the Storm Bull cultists can sense that taint. That may not be just but it is what it is. Storm Bull is neither pragmatic or just.
However, Orlanth is both pragmatic and just – far more so than Storm Bull – and Sartar was famed for both traits. Orlanth cannot sense Chaos – he judges folk on their deeds. Sartar made peace with the Telmori and ended a terrible war between the Telmori and the Orlanthi, Most importantly, Sartar ended that war in a way that all sides got what they wanted and more.
And so Sartar has a bodyguard of Chaos tainted elite warriors. Does that upset many Storm Bull cultists? You bet! Do they take action against him? Nope. Sartar has Orlanth Rex’s magic and the Storm Bull cult is small in his lands. And the Telmori in his service performed incredible deeds. They are like the berserkers who served Harald Fairhair or Hrolf Kraki – fearsome and unnatural, but they serve a just leader and thus are made part of the social order. But if the Telmori do not serve Sartar, they return to being outside of the social order and a Chaotic nuisance.
And this is an important point to make – although Orlanth is certainly destructive, he is also certainly just (which is NOT the same as being truthful or honorable). Orlanth is not pitiless or without mercy. He makes peace with his enemies in order to save the cosmos.
Wind Lord Challenges – “Lie and whimper before me.”? Yes. But what is a Chaos monster? Orlanth does not have Sense Chaos, and his cultists do not have access to the game rules.
Surly Sartar knew the Telmori were chaotic? Sartar cast Command Priest or his version of City Harmony. And said that the Telmori were victims of Chaos, not perpetrators of it. And that the Telmori would be protected by Hauberk Jon and all those who pledge to uphold the peace. Although Sartar never raised a weapon against anyone, he had plenty of folk who would do that on his behalf.But I actually kind of doubt it. Sartar also aided the Pol-Joni, who dominate the local Storm Bull cult, and enabled them to defeat the Praxians that sought their doom. And the Pol-Joni sure as hell weren’t going to look at Sartar’s gift horse in the mouth.
Sartar was a super just and honourable mensch. If you worked with him, he always came to a Pareto Superior solution, and often even Pareto efficient and envy-free solutions. Because he really was pretty damn awesome. And the gods and spirits loved him.
Is this accepted by Argrath? Argrath’s “attack” or not attack is up to your players. The Telmori do rebel against Argrath (they have a lot of 7 Mothers worshipers and a lot of reasons to hate the Jonstown tribes). But whether the Telmori are destroyed or not is an open question.
As far as Chaosium publications go, there are no Pure Ones outside of Ralios. All the Telmori who made the long march across Fronela and Peloria are descended from those who accepted Nysalor.
Another is that Lunar emissaries get many of the Telmori to rebel against Argrath and his Barbarian Horse.
And yes, the Seven Mothers is tied with Humakt for the second tier cult of the Telmori. Even if we God Learners know that the Red Moon is not directly responsible for the transformations, it does seem more than a mere coincidence. And most Telmori figure it is connected to the Red Moon.