The short answer is no. Port B ACE to the built-in ACE port of another iDR is only supported for Dual Rack setups, i.e. to expand the number of input channels.
You can internally split the FoH/Mon channels in a Dual Rack setup for independent processing, but you are still limited to <32 mix outputs and 8 stereo FX engines in total.
To get two completely independent, fully functional systems you need a Port B to Port B connection.
Hope this helps.