Hi, the minimum size of a VM snapshot if I remember correctly is 1.2GB when is created, and from here it can grow over time depending on the amount of writes it receives while the backup is running.
VMware usually recommends to stay below 80% of storage utilization. Veeam has no impact on snapshot growth, it depends on the activity while the VM is snapshotted.
EMEA Cloud Architect @ Veeam Software
Veeam VMCE #1