ok, couple disclaimers right up front:
1. I'm not yet running Observium - I've joined the list, but have yet to find the cycles to install it, and
2. I'm not an SNMP expert by any stretch
But while verifying that 'less -R' could indeed render your escape codes, it seem to me, unencumbered by knowledge, that you are missing mibs for specific items. It seems like it is returning data for basic stuff it understands, but it could simply be a confusion between net-snmp and ucd-snmp too, dunno. Hopefully you get this ironed out. Following, and interested, as I have some OpenBSD boxen myself...
-C