Sam is not evil/good, but I think she is a rather omniscient being in these zombie maps... She gives them power-ups like this is all just a game. If she plans to have revenge than why give them gifts of power? Nicoli wasn't always a drunk, The american [forget his name] has amnesia, Richtofen was the scientist who started all of this, and the asian guy is just there, I suppose. If you think about it... The Death machines you get after freeing Gersch are also a gift from Samantha... But if she was trying to catch him than why would she give you the 'best' weapon as a reward for freeing her prey?
Riddle me this: Samantha chases a scientist as what she sees as 'prey', for some reason, and then her 'prey' is freed by the people she is trying to get 'revenge' on. Why does she reward you with such good weapons?