Currently we don't provide a MIB so users can choose to organize their structure in any way they want. Moving forward in Ambari's future, we may provide an Apache MIB. I believe thats what the ticket, that you referenced, was opened for (along with the patch, README and other inform necessary for the implementation) : https://issues.apache.org/jira/browse/AMBARI-1320..
Today, we use a single OID for all of Alerts, and the body of the trap looks like this:
2015-07-22 13:28:41 0.0.0.0(via UDP: [172.16.204.221]:41891->[172.16.204.221]) TRAP, SNMP v1, community public
SNMPv2-SMI::zeroDotZero Cold Start Trap (0) Uptime: 0:00:00.00
SNMPv2-MIB::snmpTrapOID.0 = OID: IF-MIB::linkUp
IF-MIB::linkUp = STRING: "
[Alert] NameNode Last Checkpoint
Last Checkpoint: [0 hours, 43 minutes, 44 transactions]
" IF-MIB::linkUp = STRING: "
[OK] NameNode Last Checkpoint
Hope this helps!