I agree wholeheartedly Bertie that that's how it's been depicted. Although I am curious how a half-way government would be though...something between the Cardassians (who I think co-opted the Romulan identity) if only for variety's sake. But also reading all this, it would be more complex an identity than we've become used to in storytelling...why is everyone either a capitalist or a Nazi in modern storytelling? This in-between state is especially interesting when one considers that neither the commie Chinese or theocratic Iranians are simply as oppressed or oppressive as we or our media, or we due to our media, paint them as and both would do better to change their ways. I dunno. Maybe the writers just need to create a uniquely Romulan fucked-up system of governance to explain how Toreth could be so public in here dissaproval of the dreaded Tal Shiar...and one that's worse than the Cardi Nazis because badder is juicier and might explain why Vice-Proconsul(!) M'Ret would go so far as to defect.
The Romulan Star Empire could well have been like the Roman Empire. Using Shinzon and Sela as examples; a non Romulan can advance in the system. Those non Romulans advancing have to work twice as hard to get half as far. Nothing new about that. In ancient Rome a non-Roman can be a citizen and have all the rights as a Roman. The same seems to hold true for the RSE. This would not be through enlightenment but pragmatism. As for religion, if the Praetor of the moment doesn't see it as a threat to power, they'd be indifferent to it. The RSE probably would not worry about any Earth based religion. The Surakians, led by Spock is another matter. Rome had its periods of enlightened rulers like Marcus Aurelius. The RSE probably has the same. Then there were the types like Caligula. Who'd want to imagine any type of Romulan equivalent to that? Like other posters have written, the Romulans like the Romans would probably have positive influences on their tributary or subject worlds. There was a TNG novel written several years ago in which a world had to choose between allying with the RSE or the Federation. I forget the title, but the conclusion is not a foregone one.