In the final product, you could build the data center underwater in-place, and have the servers partially accessible - they only need to be connected to the structure in one end, and can be surrounded by water on all other sides. (Visual idea - the data center parts are like fingers on the main structure).
I would imagine bulkheads can mitigate some unforeseen leak. They can also be built in relatively shallow water without a substantial amount of water pressure.
