Is NAT can provide some kind of protection?

[Tarig Ahmed]

We have wide range of Public IP addresses, I tried to assign public ip  
directly to a server behined firewall( in DMZ), but I have been  
resisted.
Security guy told me is not correct to assign public ip to a server,  
it should have private ip for security reasons.

Is it true that NAT can provide more security?
Thanks,

Tarig Yassin Ahmed