Can Editor scripts be in external DLL's or assemblies?

Can I create an external DLL or assembly which can be integrated as an Editor extension? Or do all Editor extensions have to be JS or C# or Boo scripts in the Editor folder? I want to access some non-standard hardware that Mono won't let me at in the Editor is why.

As far as I know, they can be external DLLs, you just have to add the UnityEditor.dll and UnityScript.dll to your project references.