Don't DX have to be registered in Windows - if they came as just a .dll file, that is, no installer?
The trick (I believe) is to drag and drop the .dll onto a certain Windows system file, but I can't remember details at the moment and all the DX I have were "installed" from a .exe. You don't have to do that with VST, just put the .dll in a VST folder (or sub-folder within it) and point the program at that folder.
DX8 DX plugins (as in Sonar), are not supported - these are the ones you can automate, neither of course, are VSTi or DXi. Note that some FX can be instrument type plugins (I think Sonars Re-valver is one such), and therefore won't be supported either.