I have done this before quite a few times. What I did was: 

1. Export the qcow2 or raw file and convert it: qemu-img convert -f qcow2 -O vmdk
2. Import the vmdk into vsphere storage and convert it to thin with vmkfstools
3. Then create the vm definition. 
4. There will be some minor driver and ethernet type stuff to fix.

This process has worked everytime. You probably could use a tool like virt v2v or veeam to accomplish this as well.

David