isolated DC-DC converter in series
The answer I selected does not work when no load is connected


Those converters don't regulate very well at no load even when used on their own so the above is probably a red-herring: -



Below 10% load the regulation isn't guaranteed and this is quite common for many DC-DC converters (caveat emptor).


  Would connecting "Common pin" with Vout+/ Vout- via the load resistors
  not short the connection I want to make and only produce +15V/-15V
  between my ground?


No. The voltages at all the nodes from the bottom to the top are -30, -15, 0 +15 and +30. This assumes you are using a TEL 3-xx23 device.