User blog comment:Supahbadmarine/Canon Policy Discussion 2:Empire and Xenos/@comment-8395098-20131110164622/@comment-8395098-20131110175213

it is a thing, it's not immunity but it take far further corruption in order for certain creatures and individuals to begin to manifest chaos mutations, chaos space marines can actually withstand more of the corrupting powers of the warp before their bodies mutate than normal humans, on the long term this means little mutation wise, but on the short term a heretic will have extra arms tendrils ECT before a SM.

I know of one race that was dedicated to Khorne who rarely suffered much in terms of mutation but then again they had very short life spans typically dying of war at a early age.