These UnDPs poll values from the Cisco-Stack-MIB. It will return the percentage of bandwidth utilization for the backplane. Depending on which modules you have in your 6500 and the switching mode you have configured, your modules may use the system backplane or the switch fabric or both. On the node details page of our 6500s, I have a table listing the module inventory (from mtxpert's UnDP: Cat 6500/4000 Inventory (Includes Slot, serial, model and firmware version)), the Backplane Utilization table and the Fabric Utilization table (I'll post the UnDPs for the Fabric Utilization next.)
The values returned here should be roughly the same values you'd get from running the "show catalyst6000 traffic-meter" command. Just keep in mind that the UnDP values are tied to your Statistics Collection cycle, so they will only update as often as you have your Statistics Collection task set to run in Orion. I set the UnDP to keep historical data, so we could have a history of the backplane's utilization.