Check this document for AMS considerations:
There is a matrix in here that shows you the benefits of AMS/iLO monitoring on Gen8, which I think is similar to Gen9 (I have not seen this updated for Gen9 yet).
Yes, without the AMS service you cannot get the OS details since the iLO needs to communicate with the AMS service to pull this information. All you get is IP/serial # and basic model information that the iLO knows by default.