Okay. So, it turns out that the issue is that I'm running High Sierra, and that caused a known issue with WineSkin.
The GOG Support Team helped me get the game running!
This is what I did, based on info given to me, but I'm honestly not sure if #1 and #2 were necessary
1.) Install Wineskin Winery from here: http://wineskin.urgesoftware.com/tiki-index.php?page=Downloads
2.) Start the application and use it to download additional versions of Wine (by clicking +). I downloaded WS9Wine2.8 because that looked like the latest, but I'm not sure if the version matters.
3.) Now, right click the game from GOG, select Show Package Contents, go to Contents > Resources > game, right-click the game's app select Show Package Contents and open Wineskin.app (not right-click).
4.) You'll see a window pop-up. Go to Set Screen Options, and uncheck the Auto Detect GPU for Direct 3D option.
5.) I was then able to run Primordia from GOG Galaxy, and it worked!
Glad it's sorted out! Sorry that I wasn't around to chime in before the problem was resolved!