Whether using Tabcmd or REST-API, and if you have SAML configured on your Tableau Server.
However, it means that when authenticating the user account that is logging in using Tabcmd / REST API, the Tableau server isn't going to authenticate the user details against the IdP (SAML Server), but authenticate against the credentials stored in the Repository. (ie it will check the password held locally in the Repo, and not held by the SAML server)
Hope that this is clear.
All the best