If they are part of a backup chain then you will need them and easiest way to test is do a restore.  If not then you can remove them, but ensure you don’t break a chain.

You can also check under the Backup section - Disk for the backup they are for to see the properties and if they are used.

As Chris shared, only if they are part of a chain are they required. 

Unless you're in dire need to manually remove them (regain disk space maybe?), if you have the Deleted Items setting enabled in your Jobs, you can just let Veeam worry about retention and deleting them. You can read more about this setting from the link below:

https://helpcenter.veeam.com/docs/backup/vsphere/backup_copy_deleted_vms.html?ver=120