In https://www.sqlite.org/copyright.html they specifically talk about how to use SQLite in a jurisdiction that does not recognize the public domain. And major projects like Android and Safari use SQLite globally, so clearly the legal risks are limited.

Any legal risk, and Hwaci can avoid employing people from problematic jurisdictions (from their POV). I suspect there is a workaround anyway: Hwaci can require any German developers to assign copyright of code to Hwaci, and then Hwaci can put that code into the public domain.

Regardless, Hwaci mention that SQLite is “Open-Source, not Open-Contribution” and also say “the project does not accept patches. If you would like to suggest a change and you include a patch as a proof-of-concept, that would be great. However, please do not be offended if we rewrite your patch from scratch.”.