It looks like MTV assumes the default vmdk name at the time of pulling the disk from VMware, but when the actual disk has a naming different from the default <vmname>.vmdk it fails with the error:

Unable to connect to vddk data source: disk '[<DATASTORE>] <folder>/<vmname>.vmdk' is not present in VM hardware config or snapshot list

In my observation of this issue in a customer environment, their disks had the names <vmname>-000003.vmdk and <vmname>_1-000003.vmdk, and MTV generates DataVolumes to import them with the names <vmname>.vmdk and <vmname>_1.vmdk.

Both disks are created with the following properties:

• VM storage policy: Datastore Default
• Type: Thick Provision Lazy Zeroed
• Sharing: No sharing
• Shares: Normal
• Limit - IOPs: Unlimited
• Disk Mode: Dependent
• Virtual Device Node: SCSI controller 0 – SCSI(0:1) Hard Disk <n>
• SCSI controller 0: LSI Logic SAS

I am not sure about the use cases MTV covers today discovering Disks, but I found this link to VMware with describing the VMDK File Naming convention.