I found out that the backup agent doesn't support multi-nic configuration during transfer if you do integrate with Veeam B&R. It is using only one nic.
My best guest is it doesn't use SMBv3 protocol and can't leverage the multiconnection. The alternative would be to dump the backup directly on a SMBv3 share instead
of the Veeam B&R but it would break the integration on the other side.
Is it on the roadmap to support multi-nic ?