You could say that, but UltraHLE did some emulation at a much higher level, hooking OS functions that the dynarec couldn't handle and redirect them to C functions that performed their functions. From what i've understood, UltraHLE didn't bother to emulate the RSP co-processor either, but simply recognized the highlevel commands sent to it, and translated them to Glide.
Zsnes doesn't do anything similar, it's simply impossible on the SNES since there is no common OS code in games or co-processor with microcode. It would perhaps be possible to HLE the sound coprocessor in a few games but compatibility would drop, just like UltraHLE.