I have been testing backups with two linux virtual machines with vmware tools properly installed. I have enabled CBT on these virtual machines. When I browse to the cifs share on the recovery folder and windows is reporting that the size of the images folder is 650 gigs. My storage guys are reporting that I am only using 18 gigs out of the 200 gigs they provisioned for me. Is CBT doing its job?
This sounds correct. What you are seeing is vmPRO presenting the CBT Differential backups as 'Synthetic Full' images. On your target storage folder the actual utilized space is very likely closer to 18 GB, but when you look in \\vmPRO\recover\images, every job/folder is presented by vmPRO as a full image so that you don't have to worry about re-connecting the base Full backup to the Differential -pancbt.vmdk files on your own.
In a nutshell, if vmPRO is no longer managing the backups and no longer responsible for expiring the data, then you need to manually remove the backups. vmPRO won't automatically remove all the old backups if you delete a policy. Which is a form of protection anyway because you might still need to recover the data at some point.
Basically, mount the NFS datastore from some other system and delete the folders. There will be no harm to vmPRO if you do this.