Hetzner Cloud snapshoot can be an additional measure in case of total backup failover, but as @fbartels said, snapshoot could have inconsistent data and generate corrupted instance when recovery-restart.
Snapshotting an instance can be an extreme way to recovery data. Of course, cannot be the first and the right way to make a restore. If you use that feature to make it cheaper I think is not a good way to approach problem.
As @jdaviescoates said, you can purchase a Box from Hetzner and configure an extra backup, mounting CIFS directory. But also this procedure can have some risks in case of a total failover of Hetzner datacenter or connection. Best practice is to use a different provider or datacenter.
(Now I'm testing Wasabi and seems to be fast, stable and reliable, but I'm scared about privacy policy management: maybe for some configuration mistake data directory can be exposed).
Question is: @mikulabc why you want to use Snapshotting feature? To be cheap?