Split DNS. Backslash in domain name

That doesn't look good.

Please elaborate on exactly what you mean by this:

I'm using my ADSL router for internal lookups, but it returns backslashes in reverse lookups.

Specifically, why are you using your ADSL router for the lookups?

Also please elaborate on how did you set up your DNS server? Via Server Admin? Or via direct access into and editing within the DNS data files?

My confusion: I would not expect an ADSL router to be particularly involved with DNS here, and commodity ADSL routers are potentially suspect devices regardless. Though that your Kerberos is showing up oddly is, um, disconcerting.

I'd expect the DNS query to be issued from the clients on your LAN. Directly to your Mac OS X Server and its DNS server. And I'd expect to issue dig commands from the LAN clients, as well.

This DNS set-up can be generally confusing, yes, particularly when you're mixing what an ISP might document with how to get LAN-based DNS services working with DHCP servers and the usual odd-ball prompts that these various devices can display. The (dynamic) clients on your LAN can potentially involve your ADSL router, specifically for they acquisition of a dynamic IP addresses and of the IP address of your Mac OS X Server's DNS server. These references can be provided to the (dynamic) clients by the DHCP server, and the DHCP server might be co-resident within the ADSL router or might be the Mac OS X Server box's DHCP server.

Test your lookups from a client and from the DNS server itself with Terminal.app and (forward DNS) with +dig host.example.com+ and (reverse DNS) with +dig -x target.ip.address.here+, or with Applications > Utilities > Network Utility. The former is the command shell, the latter is a GUI tools.