Yes calling “Remote Desktop” requires Apple Remote Desktop to be installed. Please keep the ARD script that way.
Maybe you could add an alternative script called “ConnectWithOsxVnc” or something.
One suggestion to the ARD script: if the user have selected more than one slave when firing the script, it could maybe default to “observe” not “control” in the apple script section, so that the selected slaves would be show in one ARD window, not many.