"powered initially by gas, moving to hydrogen in future."
Leaving aside the fact that hydrogen is also a gas, powering the fuel cell by natural gas, i.e. methane, is hardly decarbonising the operation compared to using the same gas to fuel a gas turbine-driven generator. The significant question is how is the long-term hydrogen to be obtained? If that involves simply transferring electrical energy from some other source into chemical energy in the form of H2 why not use that electrical energy directly?
Fuel cells and hydrogen make sense (give or take the difficulties of handling hydrogen) where the energy is to be deployed in situations which are intrinsically disconnected from the grid such as vehicles. The only point I can see for a static installation such as a data centre is green-washing.