use
CISCO-ENHANCED-SLB-MIB
following oid will give you the operational status of all the rservers in all server farms
cesServerfarmRserverOperStatus=.1.3.6.1.4.1.9.9.470.1.1.3.1.7
possible return values are
1:outOfService
2:inService
3:failed
4:readyToTest
5:testing
6:maxConnsThrottle
HTH
Syed Iftekhar Ahmed