To clarify the post above, it now appears that the cap of 3,500 visas from any one particular country may have been hit for Iran rather than the worldwide 50k limit. It's my understanding that the Iranian applicants were turned away at the gate by State's security contractor (G4S), which itself is staffed by, shall we say, individuals with a surprisingly limited ability to communicate in fluent English. I'm still unsure of some of the details of what happened on Sunday in Abu Dhabi.
If that is the case, the Yemenis being represented by NILC may be able to proceed with their claim.