I'm about to configure MRTG monitoring for VMware performance and to hopefully resolve some replication performance issues.
Did you have any success running MRTG under VMware? I'm going to try and find a pre-built vmdk. I'll let you know if I have any success.
I run MRTG as a VM. Started with an FC6 appliance from VMTN and yum'd the MRTG package. About as easy as you can get and it works like a champ.
I would be interested in anyone gets MRTG monitoring of ESX running.