Vetting sites only assures that one of a webmasters sites is up to standard, he could have dozens of others redirecting to the casino via the vetted site and unless the casino personaly spots one of the other sites then it’s pointless.
If an aff prog actively pursues quality control after the initial vetting (ie. they follow up an any complaints about a non-vetted site) then it would work to a certain degree – but just initial vetting is pointless.
But lets face it, even those affs who obey all the rules could get rejected – many of the so called good sites are simply banner farms with a pretty face lift and offer no real original content.