This can be cheated. They could get someone else to create the Gibhub portfolio for them, perhaps a friend who's an unemployed "real programmer", just like they could get someone else to sit an aptitude test for them if only HR people are at the test and no photos are taken.
I just can't imagine hearing someone say "Yeah this guy is a great visual designer, look as his gorgeous portfolio, and look at all this great stuff he did at smashing magazine (or whatever good place for design, I don't know..) But he's not a team player, he is sceptical about doing 'pair-designing' for 8 hours a day with other randomly chosen incompetent designers. No hire."