I wish my HVAC system was SNMP monitorable.
In answer to your question though, we can monitor anything that speaks SNMP. You can either stick a raspi or something on there and write your own SNMP MIB for now, or wait, and then write a ZenPack.
There's a 4 part guide on developing SNMP Zenpacks, and related documentation here: http://wiki.zenoss.org/ZenPack_Development_Guide