Just a quick update. Five days later, and I have found that most of the time iTunes will recognize the iPad through wifi and sync through wifi.
Here is what I've done that seems to enable wifi detection and syncing on my computer (note that I use Windows 7, iTunes 11, Symantec Endpoint Protection 12.1; iPad II iOS 6):
For the iPad, I created an "allow" firewall rule on Symantec. On the Host tab I used the IP address of my iPad. For the port, I set both local and remote ports to keep open UDP port 5353.
To enable iTunes on my computer see another, shared library residing on another computer on my home network, I created another "allow" firewall rule. On the Host tab I used the IP address of the other computer (On the other computer, go to Start, enter "cmd", then enter "ipconfig", then look for IPv4). For the port, I set local and remote to UDP port 5353. This works great.
iTunes doesn't always see the iPad, even with Symanteic End Protection entirely disabled, so part of the problem is Apple's, not SEP. But "most of the time" is a lot better than "never." And sometimes to get iTunes to see my iPad, I have to restart the service "Apple Mobile Device."