Best answer by dan_ahrens
Not sure if you're still looking for a solution for this one but I came across this old thread.
The solution you want to look at is to use Bionic rules to fetch from your Account object (filtering on active accounts), and then fetch from the Gainsight system object Zendesk Tickets. Merge those two fetches together with an outer join (keep data from both sets) and match on Account ID (to link your SFDC Accounts to SFDC Account records in the Zendesk Tickets object).
Any records that have a Zendesk Tickets Organization Name, but no SFDC Account Name will be those missing the SFDC Account association.
General Bionic Rule info: https://support.gainsight.com/Rules_Engine/Admin_Guides/Getting_Started_with_Bionic_Rules