vim-cmd is a valid ESXi command. I have use it in ESXi 3.5 and 4.1 u1. I am sure it works in 4.1 without update.
Try vim-cmd vmsvc/getallvms to get powered on VMs.
Use these steps:
1. Get the VM list: vim-cmd vmsvc/getallvms or vm-support -x
2. Power off the VM: vim-cmd vmsvc/power.off <vmid> or vm-support -X <World_ID> –w <dir>
There is also a method using ps and the kill command. I know VMware has a KB on this. I'll see If I can find the KB.
Robert