If both arrays are a source and a target at the same time its called bi-directional SRDF and EMC does not recommend running in that configuration with SRDF/A.  The recommendation would be to use a set of directors for each group.  Performing a personality swap isn't affected by the director count.  
Is it possible to create and activate two simultaneous srdf-a sessions on different groups between two dmx's? Primary site:               DR Site: R1                ->           R2               group1 R2                <-           R1               group2
srdf-a between dmx's