Hi -
Local security settings are the first to get overridden by group policies followed by the order - site - domain - OU. OU policies get applied last. Yes, you could be getting hit by Default Domain policies, this is where account policy gets defined. From your Unity server, start cmd and run gpresult. It will show you what policies are being applied to your Unity server. Since OU policies get applied last, I would check to see which OU your Unity accounts are in, and see what GPOs have been linked, if any, to that OU.
Ginger