It all depends on which dual CPU one you're talking about, and what OS.
A standard version of OS X works fine on all dual-CPU G4s. (Obviously, later machines that came out when 10.2 was current require 10.2, and won't work with 10.1, though.)
If you're talking about one of your sig-mentioned systems upgraded to dual CPU, then any supported OS will work just fine.
If you're talking about a later dedicated dual-CPU rig, then it depends on which one. From my understanding, the Mirror Drive Door models can *ONLY* run OS 9 from their own custom install disc, they can NOT use a bog-standard 9.2 install disc. For a Gig-E, Digital Audio, or either Quicksilver, a standard 9.2.1 install disc should work fine. Although this is true not just for the dual CPU models, but for the single-CPU models of the same family.