Is indeed material group hierarchy exist in ECC ?
I believe you can create own custome hierarchy in SRM and upload programs rather bring from ECC .
it becomes source system of product category becomes SRM system thats all
you need development for this . Business has to provide hierarchy list and excel file and upload in to program and it must seen from COMM_HIERARCHY TRANSACTION.
BUT ONE BAD STUFF HERE , you can not change this again and you need to upload all atuffs again and deactivate above old ..
How are you?
I´ve seen some scenarios where clients have product category maintained in R/3 (SPRO / Logistics - General / Material master / Settings for key fields / Define Material groups).
You can use LSMW to create product categories.
Then you have to replicate those categories / Material groups to SRM. You can do this by Midleware (transaction R3AS). You can see hierarchys in srm at transaction comm_hierarchy.
Hope this helps,