So I found out what was going on with the "No DMD device driver found" error I was seeing. I found that I am not able to load DMDDevice.dll if the table script loads VPinMame.Controller directly, it would only work through B2S.Server.
The LoadLibraryEx call in VPM currently limits the DLL search to only the specified folder. So it would find the DMDDevice.dll, but then it couldn't locate a DLL it depended on (mscoree.dll). If loading through B2S, it - also being a .NET dll - loads this DLL first, so it bypasses the issue. Changing the LoadLibraryEx line to:
hModule = LoadLibraryEx(filename,NULL,LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR | LOAD_LIBRARY_SEARCH_DEFAULT_DIRS);
appears to take care of it and allows me to load VPM directly with the external DMD working. I committed the fix to Carny's repo.