Erm, considering that Dreadnoughts have a 0.2 damage multiplier to raid starships, I don't know if they would really be that effective. It's likely all the other ships in your fleet that take care of them Dazio.
And raid starships are immune to the effects of black hole machines, so while it would keep all the other ships that arrived with them locked up, the raid starships would be able to fly to the next system without any problems.