Even when the Catalyst 6509 runs entirely in Layer-2 and with FWSM?  Let say I have VLANs 1, 2, 3,... 10 on the Catalyst 6509 and I place these VLANs into the FWSM module.  Are you saying that the FWSM MIB will return all the ARP values in the FWSM table?

An anology to this is let say I have an ASA connected to a catalyst 3750 with multiple VLANs and I run 802.1Q on the ASA connected to a trunk port

of the Catalyst 3750 and that all the hosts, in multiple VLANs connected to the catalyst 3750, have the ASA as the default gateway.  If I do a show arp

on the ASA, I will see the MAC and IP addresses of all the hosts connected to the 3750.

Are you saying I can see the ARP table on the FWSM with SNMP MIB with the same scenario described above?

You asked whether or not the FWSM allows one to poll the ARP table via SNMP.  That answer is yes.  Now, if the FWSM does not have the ARP entries in question, then you will of course not be able to poll them.  If the FWSM is acting as a default gateway for hosts in a given VLAN, then they should be in the ipNetToPhysicalTable.