SSO with External AD together with Fusion and PBCS

Summary

Should we move PBCS to same IDentity Domain as Fusion or Leave it

Content

We are planning to do the SSO config of Fusion with On prem AD (Shiboleth), This should not be a problem but we need to do the same with PBCS as its on different Identity domain. IF we move PBCS to same identity domain as Fusion will it cause some issue ?  Or It is better.

If we move them to same identity domain , do we still need to create Users in PBCS or they will exist both sides , if they exist for both How can we assign PBCS roles to users through fusion.