They're on triple redundancy Ceph as far as I know, not geo redundant, but at that price you can buy one in Germany and one in Finland and still come out cheaper than B2.
From Hetzner's snapshot data loss email two years ago:
"The snapshot contents are distributed over multiple internal servers and data is stored in a way that allows up to two separate disks to fail without impacting data integrity. This means the snapshot can still be accessed, even if two disks fail at the same time."