Business user on separate system for PPM

Dear community and PPM follower,

I am facing a question which Needs to be answered before starting actions.

My question is related to the use of business partners (BUP0003) as resources in cProjects.

We plan to set up SAP PPM (cProjects part) in combination with CRM.

The system PPM and CRM are on separate servers.

Business partners are fully set up in CRM by replication from HR, i.e. business users are created by ALE automatically in CRM.

We don't want to create or replicate business users from HR or CRM to the PPM system.

Question:

Could we use the business partners created in CRM for PPM instead?

Is it mandatory to have business users set up in the same system as PPM?

Any advice/recommendation and hints regarding my question are welcome.

Thanks

Darijo