As described in a comment, Raddle "wants to take over the whole tree but the module crashes when we try that :-( Just go for .1.3 (.iso.org) to start with." Recently, I needed to serve up objects under .1.0 and, of course, the Raddle agent wasn't seeing the snmpgets for OIDs below .1.0. I tried figuring out why net-snmp has this limitation, but couldn't, so I modified Raddle::SNMPagent::new() to register my_snmp_handler to each of an optional list of roots.
By default, everything behaves the same as before, but if you need to respond to more than .1.3 stuff, you can do something like:
Net::Raddle::SNMPAgent->new(mibs => ['.1.0', '.1.3'])