It would depend on how someone was defining “additives” (they may have thought you were talking about “fillers” which are sometimes used in latex which is how many people would understand “additives”) but all latex needs some additional substances in the compounding formulation to foam and cure and manufacture the latex (see post #8 here).
All the latex you are likely to encounter will have been certified by either Oeko-Tex or Eco-Institut so all of it would be “safe” in terms of harmful substances or VOC’s (see post #2 here).