In this moment, Veeam Backup and Replication v12 is not supported the H3C CAS/UIS platform. If you want to backup and restore the virtual machines on H3C CAS/UIS, you can backup the VM with Agent. I tested it on my lab environment.

If you want to restore the VM (image level) to H3C CAS/UIS, you need to create the “Recovery media”. Then you can boot up this recovery meda on recovery VM and choose Bare Metal Reocvery. 

If you want to restore the volumes on VM, you can directly restore it with VBR.

I hope these information can help you!