Given that datacenters are powered by electricity, the amount of CO2 would depend on how the electricity was produced. Since the utility company providing the electricity is responsible for how it is produced any CO2 taxes should be paid by them.
Levying taxes on emissions any other way would be a nightmare to implement fairly, be very inefficient, and would be ripe for abuse and fraud. The whole carbon credit system is about the dumbest thing I've ever seen.