2010 CAS Array -> 2003 routing group connector - do you need one for each CAS server?

Just wondering about this:

• When you install the first CAS box it sets up a routing group connector between 2010 and 2003
• This routing group connector works fine for incoming and outgoing email
• When you create a second CAS server, do you need to add this to the routing group connector?

I would have thought both boxes need to have a routing group setting because if CAS01 is turned off then there is no redundancy? Or is the routing group applied to a CAS array?  I only see single boxes listed.