Re: Might it be an opportunity?
Assuming we were capable of that sort of mega-engineering project (which we will be one day, one hopes), I'm not sure it'd be beneficial as such. You'd end up coating the planet with a lot of ionised hydrogen... that said, the surface of mars is absolutely loaded with oxidised iron and other oxides of various sorts. Blasting them with a hydrogen plasma might actually liberate a fair amount of water. Possibly. I'm mostly pulling ideas out of my butt right now.