There really is no excuse for hair having a socially unacceptable aroma. Even though I don't use traditional shampoo, if my hair needs it, I will wash it with lukewarm water only, apply a rinse out conditioner, finger pick it through and then rinse followed by a cool/cold rinse.
Performing a water only cleanse leaves hair fresh and clean w/out any negative aroma.
Dry cleansing also eliminates any aromas. A dry wash with cornstarch or cornstarch spiked with essential oils leave hair smelling fresh and clean.
In my humble opinion, people who are not washing their hair either with water only or dry powder definitely may acquire an offputting scent. They need to at least do a quick water rinse or a quick powder fluff. At least that's what all my long haired or naturally textured friends do.