The ASA or FWSM have their ARP tables in MIB .1.3.6.1.2.1.4.35.1.4 , which doesn't appear to be polled by any of the built in device definitions in Airwave (I've tried Cisco Catalyst Switch, Cisco WLC, Universal Device, and Router/Switch). Most of the times I can add the device and get some information such as up/down status and interface counts, but the ARP table is never retrieved.
Apparently there should be a way to do it using the 'Custom' device and scripting, but I lack experience in this area. If anyone else has managed to do this I'd be interested in learning how.