It's quite interesting how Veeam QM uses builtin features of VMware. I made some tests on our environment.
vSphere 6.7 Essentials Plus, Veeam Backup Free (latest)
VM from server A to server B, storage A (SAS) to storage B (NFS), both storage are shared, so both servers can see them - move both compute resources and storage (impossible with vCenter Essentials Plus because licensing) -> Veeam decided to use vMotion (even if storage vMotion isn't licensed), no snapshots have been made; VM was migrated without downtime (no ping packet loss); after this, you can just standard vMotion back to server A via vCenter
VM on server A, storage A (SAS) to storage B (NFS), same as above, but move storage only -> Veeam decided to use SmartSwitch (snapshots and VM suspend), so some packet loss for few seconds appears (depends on changes made to vdisk since snapshot creation to synchronise source and target); data flow through Veeam service, so even there is additional network communication compared to vMotion => it's de facto Veeam's on the fly VM backup and restore