I'm assuming based on your question that the OS X systems are not joined to the domain? If so it is a likely a permissions issue on your DNS server - only authenticated systems are able to perform DNS updates, therefore their names never make it into DNS.
To adjust so you do not need to join your Macs to the domain or manually make the entries:
Open the DNS console.
Select your DNS server.
Select your domain.
Right click and open the general properties.
Under "Dynamic Updates" choose the option "Nonsecure and Secure".
You also need to be sure your Macs are using the correct DNS suffix. This can come from either your DHCP server or you can set it by hand.
EDIT - as @voretaq7 points out there are security implications for doing this. It is theoretically possible for someone to change the DNS name you use to access a server for example.
For test best security you would want to get your Macs authenticated in your domain. From there this issue should resolve itself.