If you are serving up NetBoot images on your network, you can tell the VM to used bridged Ethernet and image the VM over the network. Alternatively, you can use the Paragon VMDK Mounter to mount the virtual disk in the virtual machine, and use Casper Imaging to image that volume.
Not using NetBoot yet on USB key for now.
There's a video from this year's JAMF Nation that you may be interested in:
Bringing the Casper Suite to Life with Virtual Test Environments:
https://www.youtube.com/watch?v=TsSbAxQAKZM
@rtrouton I was at that session, thanks so much for that! I've been able to implement a lot of what I learned and it's helped a lot. I've even managed to snag a decommissioned Mac Pro that I'm hoping to install ESXi on one of these days...
@stevehahn, do it! It takes much less time than you think.