Not sure whether this is hydrating of leather.
I have heard about hydrating or re-hydration only for very dry leather. I find that for hydrating or rehydrating leathers, people recommend conditioners and leather cleansers, which, if you examine their ingredients, have water as an ingredient. I suspect some of that water rehydrates dry leather and the non-aqueous ingredients condition and keep the fibres supple, hydrated and conditioned.
Personally, I just clean dry, cracking leather with saddle soap and water, wipe it clean and allow to dry. I condition with a conditioning protective balm and I am good to go.