Subcontract Process - Vendor using own Raw Material

Hey Experts,

I want to know the best process to map subcontract process where the vendor uses own raw material at some instances. Basically the SFG is produced by a subcontract vendor. Thus,

SFG-Y ->  RM-A, RM-B

RM-A is sometimes provided by the company or the vendor uses RM-A from the own stock. Now how to map this process.

1-) Do I need to have 2 BOMs (one with  RM-A and one without RM-B) ?

2) If I enter the same vendor for the "Vendor" field under "Delivery Address" tab and check "SC Vend" will it work for this business process ? . In this case One PO will have two line items. First line item with item category "L" and 2nd line item for the raw material that will by vendor. ( raw materials provided by the vendor scenario)

Please advise.

Best Regards

Hussain