I got Me first Clue,
Set Manager Objects are not a .Net reference. I think Python and Dynamo dont have access to other things that are’nt .NET reference.
As long as you are using ActiveX, it can be called using python from dynamo. What i assuming you are doing wrong is the interop communication between dynamo and autocad. Have a look at linkdwg package. I believe by looking into his custom node, you will be able to achieve more than what you need