OK, I'm going to answer the question here to my knowledge so far.
The Dread Lords in my game have not increased their tech level, at least to any discernible degree in my game. I got to the point where I built up fleets of huge ships and smashed the Dread Lord ships plaguing the map, then swept down to their colony. They possessed four planets, three devoted to production, and one (the smallest) had some research buildings.
This is at a fairly late point in the game, so they have been pretty dominant up until I started unlocking some pretty powerful tech and countering their shields with missile tech.