Alex from CoreOS here: This only supports virtualbox at the moment, but we are actively working on adding VMware. Fill out the form on this page if you want us to spam you when we have the vmware image (or others): http://coreos.com/
He was talking about Vagrant (the tool CoreOS uses to distribute VM images)...
Also, I think you can just make a directory in the `~/vagrant.d/boxes/coreos` folder called "vmware" and copy over the vagrant file, box.ovf and the metadata.json. Then you just edit the metadata to have a vmware provider and the box.ovf to reference "../virtualbox/<<theimage>>"
I however do not have a vagrant vmware license and cannot test this theory.