Absolutely, the heat itself is not the problem. I read that every day the earth receives more heat energy from the sun than was ever stored in all the fossil fuels on the planet.

What's more the problem is that we could have spent that energy on much more useful things. Even if these datacenters run on green energy that means that something else isn't. And don't forget that no energy is truly green. Generation requirement, electricity transport and metal extraction for it, maintenance, nuclear fuel extraction and refinement, all these things aren't green. We can make them green as much as possible but increasing demands on energy massively is making the point of reaching carbon neutrality much harder.