AWS released a1.metal in EU regions in October 2019: https://aws.amazon.com/about-aws/whats-new/2019/10/introduci...
But not my specialty.
The Nitro card encapsulates packets from your machine so that they flow on the AWS network correctly, it emulates being an SSD, and it takes care of myriad other peripherals and interfaces that you might expect to have.
I think it also has a direct connection to the BMC or uses IPMI to reboot the machine when you are done with it (and another user takes it).
So Hetzner seems to be way off track with this claim about being the first dedicated Arm based servers in Europe.