I'm not sure what this is in response to, but I think most emerging designers would learn more if they tried to actually create their own functioning apps or websites instead of posting "fake" static UI mockups to Dribbble. Ultimately it probably doesn't matter, though: if you get hired to produce an app's UI off the back of some "fake" mockup you posted online, either you can deliver something "real" or you can't. That's really the issue: does working on "fake" mockups give you the skills to manage a real project?
I agree that people can learn a lot more working on something "bona fide" but this is a case by case topic. You can't generalize the entire community. Sometimes people just wanna practice the craft.
In terms of having the skills to manage a real project.. It all depends on whats being asked of them. Visual designers aren't necessarily always asked for UX. So what's the harm in putting some dressy pixels out there? If the client ends up being taken for a ride, then it was just a bad judgement call on their part. Smart clients can usually call bull-shit before it hits the fan.
What's this in response to?