Hi Etienne,
User Management in IBP is done through Model/Configuration UI (WebUI) which works on HANA database. I do not think IBP is yet ready to support CUA(Central User Administration) kind of functionality.
Just FYI - Under user management in IBP, you can setup roles, create users and provide them required authorizations/assign roles, create visibility filter etc. Please read more about this on help.sap.com.
Let us wait for other experts to share their inputs on your original question.
Thank you
Satish Waghmare