What are these Reavers? They appear to just be bandits. They have the same dialogue and the same names (Marauder, Highwayman, etc.) Is Reaver a Morrowind version of a bandit?

They were in Oblivion if I remember right. Don't recall them from Morrowind. Just a different faction of bandits anyways.

Wait until they call you N'wah. MW fans rejoice!

They where from bloodmoonhttp://www.uesp.net/wiki/Bloodmoon:Reaver, can't remember where they where from though. Reaver is just another word for pirate or raider IIRC

They are atmoran, they are supposed to be complete savages who pillage the north and kidnap people. Skyrim had more of a problem with them than solstheim, but I guess not anymore because they are not anywhere to be found in vanilla.

Reavers were aplenty in Bloodmoon, they're just there for simple continuity I'd imagine.