As Granite incorporates the CRX Repository implementation of the JCR API Specification it has its own user and group administration.
These accounts are the underlying basis of the AEM accounts and any account changes made with the Granite administration will be reflected if/when the accounts are accessed from the AEM Users console (e.g. http://localhost:4502/useradmin). From the AEM Users console you can also manage the privileges and other AEM specifics.
Granite user and group administration consoles are both available from the Tools console of the touch-optimized UI: