The ArtSchool forum section is where the students enrolled in Marc's art course post their assignments and progress based on the videos offered in the course. So to post there means you know what the assignments are, which imply you bought the course.
With that said, we also have the art blog section that is a more general section where you can make a topic to post whatever art project you're working on.
And in either case, you can post traditional or digital work. There's no problem with either. In terms of the ArtSchool program, there might be some exercises that are centered around tools that are specific to digital work, but in general I believe what is taught is transferable from digital to traditional.
I hope this helps!