I took a look around, Joe. Basically Boom Studios just lets people upload samples to their Facebook page. They don't offer a public critique or anything. They do post a 'Tip of the Week', something along the lines of: Composition is important it can make or break your artwork! Despite the fact that Boom really didn't define the parameters of submissions at all, most people seem to know the drill. Most submissions are several sequential comics pages. A few submissions are merely pinups, and colorists and logo artists are also submitting their wares as well. While some submissions are crude, I would say most are from pro level artists and many of those are currently employed in the comics industry or as storyboard artists. Everybody needs more work!
This is strictly for visual artists, no writers allowed. Boom states they have hired artists through programs like this before. That's not surprising at all, many are darn good.