Nothing about the ammeter wiring is unsafe as far as the way it is intended to work. The problems set in when the multiple connections in the entire circuit loosen and corrode, usually from age. The full amperage of every circuit in the car passes thru the ammeter and the firewall connectors. This is the way ammeters work. you can't bypass it with a relay. Fusible links protect the ammeter circuit from shorts, but old and dirty high resistance connections can heat up, eventually causing burnt wires and possibly fire. This is why you see butcher jobs around the firewall connectors and fusible links where someone has tried to repair faulty connections. The firewall connection is underdesigned for the amperage required and adding accessories like big stereo amps will only make the situation worse. Best solution is to map out your primary alternator/ammeter/battery wiring with the largest guage wire practical and the minimum number of connections and splices. Of course, this would eliminate most of the stock wiring which is at odds with retaining a factory appearance. Sometimes you have to make choices.
