Once I started reading other people's experience of running an exit node through that ISP (Hetzner), it turned out that the hosting company was the one receiving these reports and forwarding them to you. After it, the consequences can range all the way from warnings to physically shutting down your server until you do something ridiculous (IIRC send them a physical mail).

Since I didn't want to risk my server being shut down for whatever reason (there are some other uses of it non-Tor related, and the rest of the monthly bandwidth goes towards Tor relay), I've decided to just not run the exit node.

I'd say it's still very useful to the Tor network, since it handles something like 400 GB of Tor traffic per day.

However, it's on a purely notice-and-takedown basis, which is the DMCA of germany but more broadly applicable; if you are made aware of illegal activity on your network you must stop the activity and take reasonable measures to prevent future abuse. They can also fall under the network operator laws in which case they are not responsible for the traffic at all but I'm not sure if that is applicable to tor nodes or not.