1. Okta’s Universal Directory is a user database — sold as-a-Service — and the user management foundation for Okta’s single sign-on (SSO) platform. Okta’s Universal Directory should not be confused with a traditional directory service such as Microsoft Active Directory or OpenLDAP. Also, Okta’s Universal Directory is delivered from the cloud, it should not be confused with a cloud directory service such as Directory-as-a-Service.
2. Okta UI is the interface for UD (Central Repo). You get these information by using api as well.
3. Custom define custom user type object now supported by UD -

https://help.okta.com/en/prod/Content/Topics/Directory/directory-UD-usertypes.htm

Hi Cheena,

I had the same questions and I am sharing what i learnt.

1. How is the data stored in case of Okta UD? Can we maintain LDAP hierarchy to differentiate different set of users based on line of business etc.,?

-> Okta engineer confirmed that Universal Directory is a mySQL backed datastore accessible via the REST API.

1. Is there a way to connect to this Okta UD and view the data other than the web interface?

-> Yes for sure, I use LDAP browser like Apache and browse data like I do for Active Directory. and i can be also accessible via REST API developed by Okta

1. Do we need to define custom object classes that were defined in LDAP servers in case we need to import user objects to Okta?

-> Nope, You wont have that level of access. it's abstracted