Hetzner is about 100ms from the US east coast, which is doable. Closer to 200-225ms from the US west coast, which takes quite a bit more effort to deliver a good user experience. You'd probably want a secondary west coast datacenter/CDN.

That said, architecting your application so that all the small, latency-sensitive data was served from a CDN and all the bulk data was served from Hetzner would be a good/affordable option.