Hi Wendy,
for the scenario mentioned by Vinay PI is required, it is used for the vendor transfer from ROS to ECC.
"Also, in my original question, does Vendor replication from ECC -> SRM (update) work? What I would do is to create the vendor in ECC using the same vendor # in SRM, then replicate back to SRM, will that update the original local SRM vendor?"
Yes this is possible, but in a slightly different way. You can create your ECC vendor manually, and then you can edit the SRM supplier business partner and assign the backend vendor number on the supplier data tab under link to backend system. This will create the connection between your SRM and ECC vendors via the VENMAP table. Afterwards you can use BBPUPDVD as usual to update the SRM vendor data from ECC.
regards
Zoltan