I don't think RAR was ever ported to Amiga, so don't worry about it.
What a silly assumption, I might say
Of course almost all archivers have been ported to Amiga. There's always been RAR. Even XAD comes with RAR library... although it doesn't support current changed WinRAR formats. For them you need newer commandline rar. Heck, there is even the newish 7zip archivers for Amiga. Someone even made it as XAD client too.
