You're kidding me right?
I've fought Dread Lords since DL first release, and I know that they are actually push overs if you know how to deal with them. They tend to show up with numbers too few to be a long term threat... unless they are left alone long enough to gain numbers. If you attack them with a good mix of weapons, logistics, and some defenses, you can realibly destroy their ships. Assuming you can replace your ships faster than they can, the Dread Lords should run out of ships to defend their planets.
Once they have no more ships, you easily conquor their planet. With good soldiering, you should need nothing more than a single default transport, otherwise 2 or 3 transports should be enough.