You can actually fullly work/interoperate with older ARD client installs, at least everything I have tried seems to work.
At first I looked at the commandsin the "SEED COMMANDS" menu item in the "Remote Desktop" menu. Not sure exactly what they do, but they (at least not alone) did not fix the problem.
However, in the preferences of Apple Remote Desktop you will find a checkbox for "Allow communication with older clients (less secure)" in the Security section. That seems to have worked for me here.
This restored my ability to administer the clients without having to mess with SIP and without having to upgrade the clients to pre-release software.