Workgroup Manager will not connect from a remote machine

Setup:

XServe G4 1.3GHz/1.5GB hosting DHCP/DNS/NAT/Firewall/FTP/SMB/AFP/MySQL/Web

NAT/DHCP assigns 10.0.0.x internally on En0, EN1 is connected to the WAN (Uverse).

All functions are working as they should, except one:

I cannot connect to the server via Workgroup Manager via Server Admin tools on my Mac Pro (which is assigned a 10.0.0.x address as per my DHCP/NAT configuration). Workgroup Manager works fine on the XServe itself if I use Screen Sharing to remote into the server, but I want to be able to configure the users from my Mac Pro without having to ARD/VNC into the server.

To be clear, I can use Server Admin and Server Monitor fine to manage those aspects of the server from the Mac Pro, utilizing either Web-Server.local or the server's En0 address (10.0.0.1) and the administrator username and password; however, if I try to use Workgroup Manager in the same fashion, once I click connect, nothing happens. The login dialog stays onscreen, I never get a failure or timeout notification. The app is not crashed, I can open menus, quit app, etc just fine. It just never connects. Does anyone know how I might begin to diagnose the issue? It isn't a big deal, but niggling issues like this are the kind that drive me crazy, because I cannot see any reason why it shouldn't work as advertised.