One of the larger DCs is 7.65 GW on 8000 acres in Texas. It will radiate around 236.3 W/m^2 (compare vs 1000 W/m^2 solar irradiation). This emission continues 24/7/365, while the sun doesn't. So yes, the UHI is real.

That plus all the gas turbines powering it which release many tons of gasses.

And finally all the infrasound from the DC and its generators have impacts on humans and all creatures for many miles away.

Oh and the water consumption.