Last time we tried, a couple of years ago, it compiled but threw a "member not implemented" exception at runtime when trying to set System.Drawing.Graphics.PageUnit. The control uses it to implement the diagram's MeasureUnit property. This could probably be replaced with a ScaleTransform, but we haven't tried it and don't know if there won't be problems with other members.

If you haven't already started developing your tool in Mono/WinForms, you might consider Silverlight - our Silverlight control works fine on Mac and you can also use it for desktop (out-of-browser) applications.

I hope that helps,
Stoyan