I thought CS couldn't have it used on them. I wasn't sure about Uldavian but I seem to remember people having to use a Creatu-specific morphing potion (like Zenirix or something) on a CS first to get the GaS color to be on a regular pet THEN morphed them using RMPs. At least, that's how it was back when RMPs first came out.
A note to remember, the RMP will NOT morph your pets into CS or Uldavian ones, ever.