NFS for backups is one of the stupidest ideas I've heard, and someone doing this for a job should be fired.
- sends data unencrypted, anyone can spoof. Basically the same as if you gave anyone a readonly root access to all your computers.
- impossible to set up securely, if you give ANY write privileges, with a simple IP spoof attacker can delete/change anything
- no checksums, if errors occur in transfer, you're screwed.
A very simple workaround is to pipe the results of tar or dump or whatever into ssh. This solves the mentioned problems.