Ever since I implemented SNMPv3 on all my switch gear, the discovery of devices on other subnets doesn't seem to be working. All the client MAC addresses and IP information is blank except for the local subnet the switch is on. I've done some reading, and understood that the Mapper is supposed to at least pull the MAC address from the switch port. It that correct? I just wanted to confirm this before I continue looking for the cause of this issue.
That's correct. MAC addresses should be retrievable regardless of whether the switch is on the same or a different subnet. In fact, you can try running the Port Mapper against a switch accessible over the Internet, and it should successfully pull the MAC addresses.