Former colleagues are a rich source of help to leaders and organizations. Alumni who know the organization and its leaders especially well are in the perfect position to lend a hand in ways that no one else can. Staying in touch and maintaining alumni relationships can pay huge dividends.
This would be easy to track in your CRM or even ATS. I wonder how you’d get around code of conduct and conflicts of interest for same industry. I know this happens informally all the time.