Hi! Chassis Redudancy on Aruba 5400R zl2 Switch Series means that you deploy two Management Modules (MMs) and configure the redudancy mode of operation of the switch's managment modules either as Warm Standby or NonStop Switching: in both cases there will be an Active Management Module (AMM) and a Standby Management Module (SMM) but in the latter case (NonStop Switching) the SMM, in contrast to what will happen with the Warm Standby redudancy mode, will be continuosly synched by the AMM and the switching, during a failover AMM->SMM, will not cause disruption (this at Layer 2 level) because the failover can happen real-time.
Now, in both case, no load balancing happens among both MMs since one is the AMM and the other is the SMM (so this isn't, from the packets/protocol processing standpoints, an Active/Active mode of operation), the SMM is just synched in order to take over in case of failure or manual switchover of AMM.