I am having a similar issue on a similar OS. Not sure if it would justify its own thread or not. Did you find a solution? I am trying to configured SNMPv3 on CentOS 6.4. It is configured per the instructions at Configure SNMPv3 on CentOS 6 - Networklessons.com.
When I run snmpwalk, it works fine.
When I run tcpdump, I see three request attempts from Orion
Orion just says that the authentication failed.
I have tried every combination of authentication and encryption protocol levels that I can think of (MD5/SHA, DES, AES128, AES192, AES256) just to rule those out.
Has anyone had any success in monitoring RH/CentOS in Orion using SNMPv3?