By other switches you mean again Arubas in stack or different vendor/non stacked? I would recommend openning a support case so you would have your devices checked for SNMP compatibility.
In my environment, there are 3 instances I see multiple unique MAC addressed attached to a port. One is if it is a trunk port, the other if I have a PC attached to a Cisco phone attached to the port, and finally, if there is a 'dumb' switch attached to a port with multiple devices attached to that.
I don't know your environment, but is it possible there is a 'dumb' unmanaged switch attached to that port and multiple things attached to the unmamaged switch? Something like a commercial grade switch? We have a couple of vendors that stick those on our network for their gear. I notice those by seeing multiple MAC addresses.