Are you asking if it can provision bare metal servers with hetzner in a similar way to what it is doing with cloud servers, or if it can manage clusters on your hetzner bare metal servers (in the case of the second, a tool like Rancher might be better)
I was thinking more of the former, whereby I "bring my own servers".
I haven't really thought it through yet, whether that even makes sense.
That might be a bit challenging unless they sort out an integration directly with hetzner as I don't think their API supports anything related to bare metal provisioning, just cloud and 'storage boxes'
Cluster-api project is what you want. It's the holy grail of cluster lifecycle.