Good question. I read about that a long time back, but don't remember whether there was a way to get it to work or not. I am using an AutoMeter voltage gauge on my car with a one-wire alternator. It was a great upgrade. The one thing that I find important with the one-wire is that I can easily tell if the alternator has been "excited" properly to begin generating a charge. I ran a larger pulley on the alt for a while, and it required me to rev to about 3K to get it charging. When my carb wasn't tuned properly, and rev'ed slowly, it was hard to get the alt to charge. Luckily the gauge allowed me to know exactly what was going on with it. If it was at 12 volts it wasn't charging. If it was at 13-14 volts the alternator had kicked in.
I am guessing you already know this, but you can remove quite a bit of wiring for the voltage regulator from your engine compartment. That was a big plus for me with this upgrade.
No. You can't run an ammeter gauge with a true 1-wire setup (you'll need 2 separate wires for the ammeter). A volt gauge tells you far more than an ammeter gauge and can easily be run with a true 1-wire alternator.