In FO3, it kinda irked me that some factions just threw themselves at you no matter what. Raiders, Talons, no matter how many of them you killed, word never seemed to get around that going up against you was suicidal.
Raiders are not a single organization/faction as such though - more like indvidual groups of robbers and the like, so I don't think it's like everyone of them has heard of the player...
I read that some factions may give you tribute in exchange for mercy if they hate you and are powerless against you.
Where did you read this? Sounds sensible though - if you can 't win against your enemy, then either you try to get him to join you, join your enemy - or try to sue for peace. More sensible than throwing away hundreds of experienced men and valuable equipment at least...