I've been trying to find it in a text because I dont feel like taking a screenshot of Morrowind. But I remember when they talk about Ald'ruhn they say most of the citizens are not part of House Redoran, but live under them fine. I took this to mean that they were not part of any great houses, just normal citizens. They may like one more than the other, but are not "officially" a part of it.

that's how i took it, they live under the ruling influence, but do not wish to partake in the great house duties, or war.