If the VM shows the base virtual disk in its settings its likely a left over from a backup (maybe due to a file locking issue). To ensure that the .vmdk isn't in use by the VM, you may take a look at the VM's vmware*.log files, and - if it doesn't show up in the latest one - you may delete the file. If you are still unsure, and you can afford a short downtime, shut down the VM, and move the snapshot .vmdk file to another folder. Then power on the VM again, and if everything still works get rid of the file.
What you may also want to check is the Veeam backup server and/or its proxies, to see whether the snapshot is still mounted to one of them (not very likely though)!?
André