Hi Nandhini,
The choice of OS running Splunk Enterprise really does not matter in the montioring of the AD server. As the monitoring metrics, events, logs are all captured by the Universal Forwarder (which will be for the specific OS version where your AD is installed)
The approach I am suggesting is this. In this approach your Splunk Enterpise can be installed on any OS platform.
AD Server ( Splunk UF with AD addons) --------> Splunk Enterprise (Indexing, Alerting and Dashboarding)
The article you had linked is fundamentally different as it is considering installing Splunk Enterprise on your AD server itself, which to be fair will not be scalable as you may have many AD servers in the future.
I'm afraid that for exact differences in both approaches, you may have to read through the notes in the documentation. Hope this helps.
... View more