In short, no.
In full screen mode, iTunes locks down the monitor, taking control of all Monitors attached to the Mac. There are workarounds though.
1.) Use 10.1.
2.) Place your iTunes main window on the window you want to visuals to appear on. When you got to visual mode, iTunes will now display visuals on this monitor.
3.)To keep working in OS X while Visuals play, simply expand your iTunes window to the full height and width of your TV screen. OS X only detects for the menu bar, so, you should be able to expand it beyond the boundaries of your screen...I think. Since I don't have dual-monitors anymore, I can verify.
Just running on theory at this point.