Which famous artists use G&L guitars?

Several notable players use G&L guitars and basses including the following: Jerry Cantrell (Alice in Chains), Elliot Easton (The Cars), Peter Frampton and Peter Green.

Do G&L Legacy and Comanche guitars have non-standard tone controls?

Indeed they do. The brand uses the traditional two Tone control design to use a circuit called the PTB (Passive treble and bass). With this handy circuit you get a master treble and a master bass control for cutting both of these frequencies. This can push your tone in a number of directions and is a great asset to have at your fingertips.

What are those unusual pickups that are on models like the USA Deluxe Comanche?

These are G&L's Z-Coil pickups. They are single coil pickups designed by Leo Fender. Though single coil in sound, they are humbucking in operation. They look similar to Leo's design for P-Bass split coil pickups but retain the famous glassy, twangy 'spank' sound.