As I recall, Ro wasn't really a big believer. In "The Next Phase," the only episode that touched on her spirituality, she was aware of her people's supernatural beliefs about spirits but had always dismissed them as superstition.
Actually, in the current book continuity, the Cardassians
I can stop you there, as the context is the Cardassians as portrayed on TNG and DS9. It's a good example of a society which hasn't bought into the Federation project or their ideals, in contrast to alien societies within the Federation - like Vulcans and Betazoids - who have. The Cardassian legal system where people are considered guilty by default is exactly the sort of 'diversity' that would have no place in the Federation.
Another less hostile example are Klingons, while they have been allies to the Federation it's also clear they don't just have a different culture, they have a different legal system and overall ideology to the Federation. This is why, for example, when Riker wants to get information out of a Yridian who is distinctly not threatened at the idea of a Federation prison he raises the spectre of a Klingon one.