Sadly, there's two problems with this hypothesis. Firstly, how could such a hydrogen atmosphere form? As pointed out by James Kasting of Pennsylvania State University in University Park, it seems a stretch to think that so much hydrogen could be trapped by the exoplanet from its parent star.
Secondly, some terrestrial bacteria consume hydrogen and carbon dioxide, so if bacteria with similar metabolisms were nurtured on these kinds of worlds, they'd deplete the gas that helped them thrive. The planet would then enter a terminal phase of cooling, entombing the poor bacteria in ice.
But, as we're talking about aliens here, perhaps other primitive lifeforms might be able to avoid the same fate. Which begs the question, if these alien life forms are so different, would they even need liquid water to survive? In which case, the whole concept of a habitable zone would be thrown into a spin.
But, until we find another life form different from our own, we only have "Earth-Brand™" life to use as a template and the "habitable zone" is the place to be.