I have a C# library that give me acceso to a cloud service.
I wonder if hydra can be used to acces it directly or is necesary to do a bridge in .net to do that?
No, unfortunately you can’t do this. Hydra is a plugin framework, so it can’t just work with any assembly, it expects a proper plugins.
So, you actually will need a plugin and a custom interfaces that you will be able to use from the Delphi side.