Software update for unmanaged clients via Bonjour?? Possible?

Question

Is it possible to update using update server an unmanaged computer on a different sub domain using Bonjour or something else?
I am using the following terminal command and have changed the http:// to my server and I have tried its IP address.
defaults write /Library/Preferences/com.apple.SoftwareUpdate CatalogURL http://su.domain_name.com:8088/index.sucatalog
I also have the following services running: AFP, DHCP, DNS, NetBoot, NFS, OD, SMB, Software Update, Web (although not sure if they are configured correctly.)
I have two networks. One is for Admin and one for students. The Admin (running Active Directory) has fixed IP Address starting 192.168.1.XXX and the student one (OS X Server) has 192.168.200.XXX (Assigned by the server automatically.)
Many many thanks.

Answer 1

I would make having a DNS server (or two, for reliability) operational for the specified DNS zones (domains) as part of the plans for deployment on, like, tomorrow.   One of the few things that would be ahead of that DNS server deployment would be the plans to get Mac OS X Server to a static address.
Not having stable and valid DNS services on the network means your network can and variously will be wonky, and you can't use ISP DNS on your private LAN.
I will assume that "students.net" and "teachers.net" are bogus domain names.  (It's more clear if you use one of the officially-bogus domain names here, example.org, example.com and example.net.)  If they're not bogus domains and you're really using those names, then you don't have those domains registered, and you'll want to set up registered domains or subdomains of your school network domain name; whatever the school has registered. 
If you're the person running the whole school network here (and don't have a registered domain name), then go register a real domain for your school - we'll call it the example school, and will register example.com, and you can then use the subdomains staff.example.org and student.example.org, and have these be assigned to your two different networks.  Hosts can then be somehost.staff.example.org or anotherhost.student.example.org, for instance.  Don't understand DNS services?  Please read this.
Given you're probably going to need VPNs at some point, I'd also get your internal network out of 192.168.1.0/24 subnet, and over into a subnet somewhere in the private 172.16.0.0/12 or 10.0.0.0/8 blocks.  This because VPNs don't like having the same subnet on both ends of the connection, and most home and coffee shop networks on the planet will use the 192.168.0.0/24  or 192.168.1.0/24  subnets within 192.168.0.0/16 block.  And this messes up VPN routing.
If the sudo changeip -checkhostname command failed with an error when executed on the Mac OS X Server box (Server, and not Mac OS X client), then check the command syntax.