If the following registry key is set, we'll get some return codes back from the Unity component that tries to open the SCM on the Exchange server...
HKLM\Software\Active Voice\AvWm\1.0\Diag Level = 1
The other registry key would have to be changed back to 0, to get the AvWM to try to check on a start up.
Services running as localsystem will have trouble authenticating with off-box E2K servers that are also DCs and with E2K clusters. LocalSystem cannot authenticate with NTLM. Using a Domain Account to run the services can solve that problem.
If the services are running as a Domain Account, and there are still problems, you can try to open the SCM on the Exchange server by running as that account. Can it be opened? If not, does it give an error message? To open the SCM on the Exchange server, try the following...
Start\Run\Administrative Tools\Computer Management
Right click at the top where it says "Computer Management" and choose to connect to the Exchange server. Then try to open the "Services and applications".
In the case where a Domain account cannot open the SCM, then I'd suspect that a Domain Security Policy is causing problems for that account on the Exchange server.