I would first like to say that this is a very good start to VMware host/guest monitoring! That having been said, I have seen a couple of bugs.
* Some guest VMs are reported as "Not Running" even though they are running (and even though my custom poller says they are running).
* On at least one of my hosts being monitored, the graphs for VM CPU/Memory/Traffic were working fine one day and just stopped. (I have verified that this isn't a problem with connectivity or SNMP.)