Correct, that tool (esxcfg-dumppart) is exclusively for extracting a readable text file from vmkernel-zdumps. The preferred method for reviewing Guest OS crash dumps is vmss2core which gives you the desired crashdump info in a format readable by the preferred debugger for the guest OS in question. As I understand it, the *zdump.000, *zdump.001, etc. are trapping issues at the VM level (i.e. as opposed to the GOS).
I think only VMware support can read those gos/vmx based dumps that you are currently trying to review (hopefully I'm wrong). However, you can try your luck opening them in a pro debugger such as IDA Pro (speculation). They have a free trial.