Not an expert by any means, but do dive some. I think one concern is that not all life can easily move or be recreated. Coral reefs probably being the biggest one there. They have huge biodiversity and are incredibly important in the health of the oceans but are also incredibly fragile and sensitive. It isn't hard to imagine a few degrees difference in water temperature affecting these and they don't just "pop up" again somewhere else, they are often thousands of years old.
Most of the ocean is pretty uninteresting though, so I would hope this project is looking at installing these datacenters in deeper waters (where as you said the life can more easily migrate) rather than the shallower waters that reefs inhabit.
Most of the ocean is pretty uninteresting though, so I would hope this project is looking at installing these datacenters in deeper waters (where as you said the life can more easily migrate) rather than the shallower waters that reefs inhabit.