I dont know, but I am sure they require all sorts of disclosures and stuff. also, i wonder if a simple google search prior to this present uproar would have brought any of this out.
Can you find out WHEN (the date) that this supposingly happened and the date of when he was vetted? If it was long ago, there should be no excuse for missing that. If it is close to the date and too early for news to break, you could understand why the vetting process didn't pick it up.