From my experience the server and viewer will work fine without any of the other DLL files, but the performance is greatly improved if the ddengine dll is with the server. I have a small uVNC frontend I wrote that copies the following files to a remote computer using paexec:
ddengine64.dll
schook64.dll
vnchooks.dll
winvnc.exe
custom ultravncvnc.ini with a random password
It then starts the server as a service and connects to the remote computer with the viewer. If I remove all the DLL's it still works fine, but the performance is improved with ddengine64.dll and the ini file set to enabledriver=1. From my experience the ddengine.dll is required to use the 'Capture semi-transparent windows' feature. Hopefully Rudi will answer your questions with more clarity though.
You can see my utility here:
http://oldnesjunkie.duckdns.org/vnc.phpIt will connect to either 32 or 64 bit remote computers, though the app itself will only run on 64-bit.