there is nothing stopping you from installing on CentOS. During the installation you will be told that you are using an unsupported OS.
Any issues that would arise from the use of CentOS instead of RHEL are not included by support. We should still make best efforts to ensure that it is not a usage/code issue, as well a having reasonable suspicion that the OS is truly at fault.
Strictly speaking, being a VMware Employee, I cannot condone going against the supported platform recommendations.
However, in more recent versions, I personally haven't seen problems directly related to the OS. vCloud is a java based application, and is paired to a specific version of Java which is provided by the installer. So we don't even use the system version of Java to create variance.
too long, didn't read = you can, but shouldn't.