Personally, I never considered the things in FO3 to be "true" super mutants. They're a different color, have different physical characteristics, well...everything. I like Fawkes' term 'meta human" because it implies they are merely just another abomination that wanders the wasteland. It might have worked better if these "meta humans" were the unexpected result of a different biological agent (not FEV in any form) and originated from say Raven Rock or some other military base. They would not have been the superior threat they make them out to be in the game, but rather scattered, largely disorganized bands that acted as just another nuisance. But that still doesn't work because 200 years later, disorganized bands of creatures that are low in number and can't reproduce should have died off completely. So in conclusion..no the SM's added nothing to FO:3 other than cheesy cannon fodder with no back story.