Hi Denis,
You can have both scenarios, materials from ECC and create new material in CRM. is not needed to create a new hierarchy for products created in CRM.
1. In trx. comm_hierarchy you will see the hierarchies created form ECC. In hierarchy R3PRODSTYP create your new category for materials created in CRM, you can also add new set types if it's required. NOTE: Don't change the categories replicated from ECC only create new ones.
2. Assign number range to the category created in step 1. NOTE: Only assign the categories for CRM materials, don't add the ECC categories.
3. Ensure the hierarchy is assigned to CRM application.
4. Create a new material in CRM.
I hope this information help you.
Regards,
Jorge G.