It looks like the folks over at CoreOS have now also produced an OVA image which can be easily imported into a vSphere or even vCloud Air environment. Previously, it took a few addition steps to convert the "hosted" disk image originally meant for VMware Fusion/Workstation to properly work in a vSphere/vCloud Air based environment. The CoreOS OVA is currently only available in the CoreOS Alpha channel for the "Production" image which also includes VMware's open-vm-tools and the latest release as of today is CoreOS 554.0.0.
You can using either the vSphere C# or vSphere Web Client to import the OVA or you can automate this simply by using command-line via ovftool. Here's an example snippet that you can run directly against an ESXi host:
/Applications/VMware\ OVF\ Tool/ovftool \ --name=CoreOS \ "--net:VM Network=VM Network" \ --datastore=mini-local-datastore-2 \ --diskMode=thin \ 'http://alpha.release.core-os.net/amd64-usr/554.0.0/coreos_production_vmware_ova.ova' \ 'vi://root:*protected email*'
You can also import the CoreOS OVA into vCloud Air's but you will need to connect into the vCloud Director interface to upload or you can also use ovftool. For more details on how to import using ovftool, check out their documentation here.
Here's a screenshot of deploying CoreOS from a vCloud Air Catalog:
The "Production" CoreOS image does not contain insecure SSH keys as the "insecure" image and so you will still need to create a Cloud Config ISO if you wish to further customize the image including login credentials. You can take a look at the script I had created for deploying CoreOS from the Stable channel and for more details check out the Cloud Config documentation as well.