I believe to avoid this error message, you will need to configure Veeam to call the System Provider / Microsoft Shadow Copy Provider instead of using any hardware provider it finds.
Veeam > edit volume settings:
Backup Infrastructure > Managed Servers > Manage Volumes > Edit > VSS provider: Microsoft Software Shadow Copy provider 1.0
I would also suggest creating a support ticket with our support team so they can investigate the error further if required. Depending on your location you can find the correct toll free number here Customer Support | Nimble Storage.
Hope this helps