Not if the datacenter itself is operating at the same internal pressure as the water around it

Interesting point. But also consider:

1. pressure may compromise the electronics

2. water pressure increases very rapidly with depth. You'd have to pressurize the data center with a liquid with the same density

3. even a small differential will produce leaks

Air (or rather, nitrogen -- oxygen at that pressure is something you'd rather avoid) can be pressurised to that degree too: https://en.wikipedia.org/wiki/Moon_pool