I've been digging into SureBackup a lot over the last few months. Just so you know, it isn't doing a full restore of the VM to run the verification against, it is mounting the repository as a NFS datastore, so only the deltas while the VM is being powered on the isolated environment are being written to your production storage where SureBackup is running.
Also, when running SureBackup, only those VMs you include in the "Application Group" are kept running during the entire run. For me that are my Domain Controllers only. Then you add Linked backup jobs to SureBackup and you can configure how many of them to start at a time. So if you have 2 Domain Controllers backed up by Veeam, you could have SureBackup keep the 2 DCs running for the entire duration, but the primary disk is being read directly out of the repository and only the changed blocks while the job is running are written to your datastores, and then however many VMs out of your linked jobs are started at a time. I run 4 at a time, and when one finishes, it powers down the VM, removes the delta files, and then powers on the next VM out of the backup job.
So you don't need full compute capacity at your DR site to be able to use SureBackup to verify all of your VMs.
I'm testing 500 VMs daily on two hosts that are also running production workloads without a problem.