Aliens would need an oxidizer to metabolize as well, even if that oxidizer isn’t oxygen. If they want to actually efficiently get energy out of things, it’ll need to be a strong one. Even fermentation is a oxidation-reduction reaction that just doesn’t use oxygen.
https://en.m.wikipedia.org/wiki/Oxidative_stress#Diseases
Antioxidants may help with some of those conditions, but others are based on such underlying dysfunction that it would be like trying to bailing out a boat with big hole in the side. They’re just not gonna do anything for you.