I am using KWin (4.11.11) standalone on Ubuntu, and would like to be able to disable moving windows via mouse drag (which I was able to do in Compiz). Specifically dialog/child windows, which will get triggered to move when I click anywhere in the window. Is it possible?

Yes: Systemsettings->Application Appearance->Style.
Click on the "Configure..." button next to the "Widget Style" chooser, and change the "Windows' drag mode" there to your likings.