whodares2: Do you know if there are aspects such as weapons, skills or classes that could be used in the core game? If so would this version then work with the other platforms?
As each game is stand-alone, there are no enhancements made available to other games in the series out of the box. There is a way to copy some of the files from Shadowrun Returns into the install folders for Dragonfall Director's Cut in order to play the original game in the improved engine of the second game. You can get more information on that
HERE. Whether or not it will work between a Steam version of SRR and a GOG version of DF:DC, I am not sure. I don't think it would hurt to try it though.
whodares2: I guess that galaxy would solve that being cross platform and all.
GOG Galaxy allows you to play games online with Steam users. It does not allow you to access your Steam library, achievements, trading cards or other aspects of Steam. The two services are completely separate aside from the multiplayer cross-compatibility feature.