So... Uh... are the Kett in Andromeda supposed to be like the Romans in Gaul?

I think it's a fair point. As I said in another post, Rome is the definitive empire in western thought. It's no wonder that both Hitler and Napoleon tried to emulate the empire in some ways. 

And this reflect in fiction as well, just look to Dragon Age! or Skyrim, or Game of Thrones.... 

It's true that there were many empires in history, and they were similarities between them (and Rome's). But I think the Senate thing is a really strong nod to Rome, if you think other BIG empires before the last 200 years or so how many of them were rulled by a senate? You could say the Athenian empire was democratic, but it can barely called an empire.