In fact, Moghedian's sending them there might have been some of the "good" had done by accident which is the reason given why she still lives. For whatever reason, she sent those two to Ebou Dar, so they were well placed to search for the cache. For all we know they might have been looking before Nynaeve & Elayne were ever sent, having been tipped off by their masters who in turn were alerted to the existence of the cache by Nynaeve & Elayne relating their dream.