Hetzner is not US-headquartered, so I'd say it should not be possible for the US government to make Hetzner turn out data from its EU locations.
They will most certainly be able to make the US subsidiary of Hetzner turn out any kind of data it technically has access to. But if Hetzner is not entirely stupid (and they are usually pretty smart) they set up their internal networks such that the US admins cannot access data located in the EU.
The problem with EU subsidiaries of Amazon and Microsoft is that the principal corporation is located in the US and subject to US jurisdiction, and that eventually, the owning company is always able to make a subsidiary comply with its demands, so it's virtually impossible to set up an impenetrable barrier between them. It's the other way round with Hetzner. A subsidiary can't command the owning company around, not even if the US government wants it to.
They will most certainly be able to make the US subsidiary of Hetzner turn out any kind of data it technically has access to. But if Hetzner is not entirely stupid (and they are usually pretty smart) they set up their internal networks such that the US admins cannot access data located in the EU.
The problem with EU subsidiaries of Amazon and Microsoft is that the principal corporation is located in the US and subject to US jurisdiction, and that eventually, the owning company is always able to make a subsidiary comply with its demands, so it's virtually impossible to set up an impenetrable barrier between them. It's the other way round with Hetzner. A subsidiary can't command the owning company around, not even if the US government wants it to.