I have used hot water at times both for restorations and for maintenance. I do think it cleans well. I also think it swells the mortise, so I prefer to keep the stem in place when using hot water, if possible. Hot water will tend to precipitate oxidation in vulcanite that's near the surface, but I don't think it causes oxidation. As for water versus alcohol, water is a smaller molecule than alcohol, so it will absorb into briar more readily than alcohol. I imagine that means a greater potential for removing soaked in tars and also for swelling fibers. Does it swell fibers significantly more than alcohol or the moisture that occurs during smoking? Probably not for a 30 second rinse.
Ironically, I've also had mortises swell from dry heat and adding moisture actually helped the wood return to its original state. I discovered this while trying to rid some pipes of a musty aroma using low heat from an incandescent lamp.