Are they just Solstheim's version of bandits (No real backstory)? Are the names just a shout out to "Firefly/Serenity?" Or is there a real backstory to their purpose?

They are Solestheim's Versions Of Bandit's yes.



As for Backstory and other things, I don't know

No one has talked about them in Forums or game

I believe their just Solstheim's version of Bandits too.
None of the NPC's (that I know of) mention anything of a Backstory to them. The most I gather from NPC's is that the Reavers are a right nuisance...

http://www.uesp.net/wiki/Bloodmoon:Reaver

Read the note on this article, and then the attached wikipedia article.

They're just Skyrim's bandits (And you'll probably learn something about the origins of the term Reaver, too)

I'm sure there's a journal or something on the island that explains a bit about them. Somewhere ...

Oddly enough, I was just thinking about this, and I'm SURE I found a Book or a Journal on Reavers...

They were once men who lived on the fringes of space...oh wait, wrong series