Hi Eric,
I am not sure whether I understand your question but general rule is that you can mutually replicate only those relationships (and also roles), which are customized in both systems.
CRM can have some other roles that are either custom made or needed for some CRM-specific scenarios. The same is for ERP. So only relationships that belong to union subset of TBZ9 of both CRM and ERP should be replicated.
Does this answer your question?
Regards,
Dawood.