First, AC doesn't work directly on AC. But, he should be able to use it if it is open on the server.
I personally would never let someone log into my office network. Granted Apple doesn't have many viruses due to its low market share, but still.
If he can't even see your server, then it is a network issue. Is the server giving out DHCP addresses. Otherwise, my guess is your computers are on a subnet like:
192.168.16.x
255.255.255.0
192.168.16.1
Which would mean he would need to have his NIC set to that subnet.
Why does he need to have his own computer? Why is he not logging into the computers in your exam rooms. Give him his own account or let him use your password. You can always change your password for the month.
