BESR (now called SSR - Symantec System Recovery) can only do a backups as if the VM is physical machine with SSR installed directly on it - it does not support any vStorage requests
BE can use the AVVI agent to do vStorage Backups (or you can use traditional agents inside the VM if wanted)
General (not specific to VMware differences)
BE can do disk and tape based backups, SSR is disk based
BE can do DeDuplication, SSR cannot
BE is a file level product (although not with VMware) SSR is a block/image level product
