Most Malkioni are far more concerned about heretical sects of Malkionism than about non-Malkioni subjects. Arkatism or “the Stygian Heresy” is considered one of the most heretical outgrowths of Malkionism.
So for example, when the Seshnegi conquered Safelster, the Orlanthi, Aldyrami, followers of the Old Gods, etc., were likely left alone. Orlanthi warriors could become horali or dronari and keep their cults, Issaries cultists could even claim descent from Talar and become low-ranking talars. These people had to declare loyalty to the King (later Emperor), temples had to pay a special tax, and so on, but were basically allowed to practice their traditional rites unmolested.
The same tolerance did not apply to wayward Malkioni – especially wayward zzaburi. Arkatism was viewed as a heresy, and followers were accused of consorting with Darkness demons and worse.
Modern Rokarism worries about Arkatism, Hrestol-worship, God Learnerism, Galvosti, Boristi, Red Goddess worship, and Chaos worship. That’s what the Watchers are looking out for. They don’t worry that much about tributary tribes worshiping Old Gods or Lightbringers.
Of course, in the Third Age Malkionism has largely been in retreat, and few Malkioni in Genertela have many non-Malkioni subjects.
That being said, Malkioni rulers are known to destroy temples that are perceived as being overly powerful, rebellious, or threats to them. The Malkioni destroyed the great temple of the Old Gods at Hrelar Amali, destroyed Arkhome, Basmol, and others.
As we know, from time to time, assemblies of zzaburi and other Malkioni leaders have periodically convened to settle doctrinal and disciplinary disputes and to revise and correct the contents of key texts. Typically they try to preserve the teachings of Malkioni, Hrestol, etc., determine and promulgate the canonical texts, establish rules for castes, resolve disputes between groups, etc. Several have been convened to purify Malkionism of falsehood.
These assemblies are usually hosted by a powerful talar, who is expected to reward the final outcome of the assembly. Pretty much anyone who can assert the right to be there can go – but then you have to prove you are a zzaburi. Some get kicked out of the assembly – the host might ask what is the teaching of Malkion on a subject, and if you “get it wrong” you and your followers get expelled by the rest of the assembly. Lots of that sort of thing. If it is a small group that gets expelled, like the God Learner followers of Galvost or Borist, they might end up forming a sect considered heretical by other Malkioni. If it is a large enough group, they might be able to claim the assembly itself was heretical and we end up with a schism or even a civil war (think a “fitna”.)