I am also having some problems like you.
Though I observed that by uncommenting the line "#COMMUNITY public public noAuthNoPriv 0.0.0.0 0.0.0.0 -" in /etc/snmpdv3.conf, and restarting the snmpd service I got the needed snmpv3 response from the AIX server or other AIX servers. But in Solarwind, after a couple of trials, I noticed setting Solarwind to snmpv1 with the community string above gave me the information on these servers.
Have you resolved yours yet?