Never even heard the term Hydropunk before. If there is such a classification, wouldn't it just fall under Steampunk? Steam is essentially just water, correct? The only way I can envision Hydropunk technology would be in the form of waterwheels and gravity/kinetic water structures, i.e. waterfalls and grand wheels. Though it would just inevitably become Steampunk or down a different path into Fantasy altogether.
Bioshock is a spattering of many technologies, designs and art forms. The thing about Bioshock though, is you can imagine Rapture without the fact of it being underwater. There are times you forget that you're many fathoms into the abyss, which was kind of the point I would imagine. It sets up the atmosphere, and toggles a few buttons in your psyche, but overall the underwater bit in Bioshock is mostly unimportant, in my opinion.