Never had an A/UX installed machine, nor seen one… so I only guess that as long as the A/UX machine is online or properly connected to your local network, there's no reason it wouldn't work.

How does the A/UX network settings look? Does it have some kind of chooser?

I'd first try to ping or telnet the OS X Mac from A/UX one…

Edit: maybe the A/UX section of the forum would have been a better place to ask!