I was just following up on the Nyko Frontman guitar problems this week and discovered that a new fix has been posted in the official PS3 forums. Fixing the problem is so simple and only requires one Dualshock/Sixaxis controller instead of two.

Turn your PS3 on with it's controller. Then turn on the Nyko Frontman. The LED will turn red.
Next, unplug the guitar's receiver from the USB port with the guitar itself still on.
Plug the receiver back in. The guitar will automatically resync and should turn blue.

It should work fine from that point.

Thanks to PS3 forum member Lightness777 for discovering this fix.

Update: If you're looking to get your Frontman working again, you're out of luck. Since Firmware 3.50, unlicensed controllers, including the Nyko Frontman, no longer work with the PS3.  I apologize for being late on the gun with this one.