Courts in Germany have ruled that you can not add additional clauses to a contract after the contract has been signed, e.g. the purchase has been made.
So unless Hetzner is buying directly from nvidia, nvidia has no way to enforce such a clause. And when I buy a nvidia card at any retailer in Germany, I will not have to sign a contract that obligates me to not use it in a data center - heck I can just take the box off the shelf and pay in cash without having to sign anything.
So anything they put into the EULA is void as it is only known after the time of purchase.
The EULA is attached up the drivers. Newer versions of CUDA often require newer drivers, so you bump into the issue regardless of when you buy the GPU.
Maybe that is the issue?