Yes, you can download the GameRoom on a Mac. Here are the system requirements available for this:
Windows® 98/ME/2000/XP/Vista/7 or Mac OSX 10.0 or greater
128 MB Free RAM
15 MB free hard disk space
Pentium® III 500 MHz (Windows version)
DirectX® compatible sound card and OpenGL® video card (Windows version)
As you can see, they specify that you'll need a Mac running OSX 10.0 or higher. However, the download will unlock after you purchased it because it's using the commercial license. To find more about it, visit its official website.