Question

Is it possible to add NuGet packages to FlexiCapture 12 project?

Answer

FlexiCapture does not support NuGet packages. The workaround is to use them in  .NET libraries. 
Compiled DLLs can be added to FlexiCapture as an external assembly and called from scripts.

IMPORTANT: FlexiCapture supports 100% managed code assemblies only. DLLs with embedded non-managed code and just non-managed code DLLs are not supported as well as any types of resource or auxiliary files.