I have very broad view that Redhat Directory Server, 389 Directory Server and Centos Directory Server are all the same. It's just the support you pay for on the RedHat version.
Is this true? Are there any differences between Centos DS and 389 DS?
This is indeed the case. 389 is the parent project for these services. The name was changed to that to divest from the branding of being "Red Hat" and to encourage adoption across other flavors of Linux.