Hello CK,
On the Catalyst 3750, the stack master handles the SNMP requests and traps for the whole switch stack.
The stack master transparently manages any requests or traps that are related to all stack members. When a new stack master is elected, the new master continues to handle SNMP requests and traps as configured on the previous stack master, assuming that IP connectivity to the SNMP management stations is still in place after the new master has taken control.
So to answer your question, with the OID for CPU and Mempory usage the switch will return only values for the active master. The other stack members are hot standby and do not produce SNMP information for CPU and/or Memory.
HTH
--Leon
