Hi Dave, I am researching this further, but i am pretty sure that your suggested configuration will work with a gateway server.
"Shared folder repositories, EMC DataDomain and HPE StoreOnce cannot host Data Mover Services — Veeam components that establish a connection between a backup proxy and backup repository (in case of backup jobs) or between backup repositories (in case of backup copy jobs). To overcome this limitation, Veeam Backup & Replication uses gateway servers.
In the backup infrastructure, a gateway server hosts the target Veeam Data Mover. Veeam Backup & Replication establishes a connection between the source Veeam Data Mover and target Veeam Data Mover, and transports data from/to backup repositories via gateway servers. "