if someone else is connected via ARD to the same machine, you might not be able to connect
Probably the best thing to do is try it for yourself and see if it's workable in your situation.
If you know who the connecting offender is, you could use your ARD to quit their ARD or chicken VNC
session which should give you back control
There is a command line that will restart the ARD client,
which restarts ARD client side. You can use ARD to send this command to client machines
sudo /System/Library/CoreServices/RemoteManagement/ARDAgent.app/Contents/Resources/k ickstart -restart -agent
you can also use it to stop, start ,user access, control etc ARD client side