They were OK with me running Ethereum testnet on their servers, but I have a 12+ year business relationship with them. That said, Hetzner will wield the banham

They were OK with me running Ethereum testnet on their servers, but I have a 12+ year business relationship with them. That said, Hetzner will wield the banhammer whenever you do things that interfere with their network infrastructure, so port scanning or connecting to many potentially unroutable IPs is a sure way to get your server taken offline. And I believe most if not all cryptocurrency networks run decentralized with P2P connectivity, which means they would cause a high rate of unroutable connection requests. Also, they can't really offer a beefy server and free HDD replacements for €50 monthly if too many people abuse it and run Chia. So as a current customer, I'm quite happy that they keep the noisy neighbors out ;)