well if i got you right, then you want to do backups on image level. so the whole vm as an "image" (vmdk files, vmx files and so one). If yes, then you need an online extension license for each phyiscal vmware host. if you want to recovery individual items from those backups (for example an excel file) you need the GRE license as well.
the other thing is, you do two backups. one is the tradidtional way with installing the dp agents on each virtual machine. then you can do normal file level backup and single itrem restore.
and in advance to that, you configure an image level backup (VEPA -> vStorageAPI) to backup the whole machine (vmdk, vmx...). So in case of a complete vm restore you can use those backup.
-> if you do this so, you need double space on backup system