Thanks David, I'm not sure what reference code I must have found where it was using \ , but my understanding is \ is escaping the backslash so it's a literal backslash? If one \ is used the remote doesn't load. The forward slashes do make more sense though so I'll adjust.
However the os.script workaround works correctly as is even with the double backslashes. The issue I'm having is the first code snippet doesn't work which is the documented method. Is the libs.server.run("Unified.USB-UIRT", "uuirt", "xxx") code currently working?