THey have very particular clothing rules that are open for interpretation depending on the  mood of the bouncer.  Had a female friend who was dressed very swankily in a matching shawl/tam combination-and no, she didn't look like a "professioinal".  Bouncer denied entry because no "hats" were allowed.  Sure that the rule was put in place for greasy baseball caps and to have an out to stop locals in gutras, he just didn't have the experience to judge what was appropriate.  She took her tam off and was allowed entry-no problem.

I'd be extremely surprised if there was any sort of ban on any nationality, but perhaps on individuals dressed or acting a certain way, and perhaps they often appear to be of a certain nationality.