ACI switch firmware is having problem retrieving config from MGMT port. If you configure it while switch is running NX-OS and then covert to ACI, IP will stay on that interface but ACI firmware will not be able to recognize it and APIC will inform you that OOB IP is 0.0.0.0. However, if you ping it or ssh everything works fine. This is true for many versions I tested so my guess is that it is not easy to fix.