Chris,
You both the chassis have DFC euipped modules or only one chassis has that?
Anyways,If you have a DFC installed on the line card it will download the L2 and L3 tables on it self and do the local re-writing of the packets.If you have a L2 link between the two chasis, DFC will do the local look up of the frames and will send them directly to outgoing interface without talking to Sup32.The traffic will not be processed by the Sup32 incase of a DFC installed. However, there could be some situation where the frames might hit the Sup32 for processing.
HTH,Please rate if it does.
-amit singh