Yes, users should be able to use a single Okta application for all workspaces, regardless of whether the Unity Catalog metastore has been applied or not. The Unity Catalog is a feature that allows you to manage and secure access to your data across all Databricks workspaces, but it doesn't directly affect the Single Sign-On (SSO) login experience.
The SSO setup is independent of the Unity Catalog and is configured at the identity provider level (Okta in your case). Once SSO is set up, users can use their Okta credentials to log in to any Databricks workspace that is connected to the Okta application.
Before enabling Unified Login, you should ensure that all users have been onboarded to the Okta application and are comfortable with the SSO login process. You can also provide them with documentation or training on how to use SSO with Databricks and Okta.