Virtual machine is fine. With that said, it is considered a best practice to have vCloud Directory run separate from resources it maintains. The thought process is that this help isolate components to reduce accidents. In addition, you mentioned CentOS. Please be advised this is not currently supported.
Some links that might help:
- http://kb.vmware.com/kb/2034092
- http://www.vmware.com/files/pdf/techpaper/VMware-vCloud-Director51-Perf.pdf