No, it will not stunt growth.
In fact, cannabis will produce more trichomes in an arid (dry) atmosphere than it will in a humid one.
In over 35 years of growing, in my country, I am yet to meet anyone who uses any sort of humidifier when growing indoors.
Most Indicas come from the Middle East, places like Pakistan, Morocco and Afghanistan, places with nearly zero humidity during flowering.
Most Sativas from the tropics are grown during the "dry season" when there is very, very little ambient humidity.
Your plants will be just fine.
Hope this helps, Organoman.