Yes, appropriately certified RO systems can reduce nitrate/nitrite. Verify an exact NSF/ANSI 58 nitrate/nitrite claim and test well water because nitrate concentration can change over time.
Why carbon is not enough
Activated carbon is useful for chlorine and many organic compounds, but nitrate is dissolved and typically requires a different treatment mechanism.
NSF/ANSI 58 includes nitrate/nitrite reduction
Nitrate/nitrite is an optional performance claim under NSF/ANSI 58. Many certified RO products carry it, but not every Standard 58 product automatically does.
Private wells need ongoing testing
Nitrate can enter groundwater from fertilizers, septic systems and other land-use sources. CDC includes nitrate among chemicals that can contaminate tap water.
A treatment system should not replace periodic water testing.
Point-of-use vs whole-house treatment
RO is commonly used at the drinking-water tap. Whole-house nitrate treatment can require different system sizing and operating economics.