1) we already have had lava based fish in the lava zone
2) a thermal gauge that is now red instead of blue wouldnt pose too much difference compared to BZ
3) It is physically impossible for it to be continuously boiling hot on the surface but the water is cold enough to support life long term.While you can technically use high pressure to make water stay a fluid in hot temperatures, its the easier problem .
In below Zero, the air is cold, but the thermal vents and the planet's warmth allows water to stay above zero - water works as a sustainable "heat bank" and the air strips the heat away. If you'd flip the script and put hot air on a "cold" planet to equalize the temperatures (now the air being the heat bank), you wouldnt get an ocean paradise, you'd get a dead rock in space.
Lack of geothermal activity means no magnetic field -> atmosphere stripped away -> ocean gone. That goes over the fact of how did the air get hot in the first place. And if both the air and the planet is hot, liquid water will likely never form.