Use .net 4.0 unsupported mono libraries via plugins

I am wondering if it is possible to use .net libraries such as speech or synthesizer as a loadable plugin since Unity/Mono does not support it natively.

I've read the managed and native plugin documentation but it wasn't clear if a managed plugin can use the other libraries or not. Or if a native plugin can be created in C#.

So my question is: Does a managed plugin allow you to use native .net libraries on windows, or is it still limited to what Mono supports? Also are native plugins allowed to be created in C# and does it allow access to .net libraries not supported by mono.

Thanks