It depends on why you NAT’d the internal addresses? What services are you exposing to the public? What do you want the public to know about those hosts/addresses? You must have DNS entries to support SMTP for sure, but if you just want visitors to go to a webhost you have, then they can use the IP address but that is a lot more difficult to remember than a DNS name.
I guess part of the reason you have not gotten a response is that since you seem savvy enough to understand firewalls, NAT and mapping IP addresses to the public IP address space – then you should understand DNS and when and why you would want to create public DNS entries.