AFAIK Kato uses 0-12 volts DC like all other manufacturers.
The voltage probably goes from 0 to 3 or 4 volts in a single leap when
the spped control is turned.
One difference between Kato and other brands is that where most brands
use 16 volts AC to operate the point motors of turnouts (3 wires where
the return is "commoned" for two solenoids) Kato uses 12 volts DC and
only 2 wires between the point switch and the point motor. This can be
replicated using any brand of transformer/power supply but requires a
small knowledge of electronics and the Kato wiring schematic.
No, there is no problems. Kato N scale trains are designed to work in a
a standard 0-12VDC operating range. Same as all the other N scale
trains manufactued since the beginning of N scale.
But as Greg mentioned, Kato Unitrak accessories (not the trains
themselves). have an unusual design.
The only other issue I've heard of is that early (non LED based)
lighting units have been known to heat up enough to melt the model's
roof when placed on a DCC track (because DCC supplies more than 12V).
But this is not a problem on any standard N or H0 DC power packs.