Considering most believe that Nomz are evil, Order propaganda was well working =).
It is like a medallion with 2 sides, each claiming the other side to be wrong =). Nice game dynamics.
Also saying that something is incorrect in a two sided dilemma would be wrong as wrong in a story driven universe where story is being handled multi-headedly and from different perspectives, turns out to be yet another perspective totally.
Therefore, yes - Nomads are evil, and no - Nomads are not evil. Its only about your perception IN GAME.
OORP wise, they are just another species with their own agenda.
Reapers of Mass Effect is a different thing. Its like "Harvesters" coming to crop the fields. There is no conflict of interest as in occupying the same space etc. Its more like "Santa's back in town!"