The marketing email released today, May 31st, said it was compatible with Mac OS. I bought the game, and the profile now says it's only compatible with windows. What do I do? I tried the support link, but that keeps saying I need a dxdiag file from a PC to submit my query. I've got a simple question that doesn't require anyone to know the performance specs of my computer, and I can't ask it because they require a dxdiag file. Seriously p****ing me off right now.

That's odd because it says that the dxdiag submission is optional. However I also haven't had the greatest of experience with GoGs support in the past so it could be very well not working properly.

Try this one:
http://www.gog.com/support/contact/other_questions_issues
Since its a basic contact and not game related it doesn't even have a dxdiag upload prompt.

Try again contacting support as Etdn says.
However the game apparently could run on MacOS: check this video.