Nope. The Amiga versions of RapaGUI are just like MUI Royale but with the same syntax as the wxWidgets based versions. They're all the same type of plug-in, patching all the same function interfaces.
AFAIR MUI documentation says, that every Task/process may only own one MUI Application Object. MUI Royale has one, and Amiga Implemantation of RapaGUI internally two...