Only running under Rosetta. You cannot load PPC code into the memory space of an UB running nativly on Intel. If the plugins run as totally independant programs they'd be fine but I'm 99% sure that's not the case.
That's what I ment. CS3 would have to "fork" a process that was a wraper around the PPC plugin and pass information via some kind of message passing, perhaps a pipe. Will Adobe go through this effort? Would be be fast enough to make it worth doing? Better to simply replace the plug ins.