OK that confirms basically what I've received from another client as well. This does in fact appear to be an ices issue. As Karl noted in the thread carlosjpr linked to previously, a defunct process indicates a problem in the *parent* process.
Taking two of your processes as an example:
1395 19914 Z [php] <defunct>
1395 19916 Z [ices] <defunct>
...these zombie processes are owned by PID 1395... which is:
1 1395 S /usr/local/ices/bin ices -v -c /home/centovacast/vhosts/yahweh/etc
...ices. So ices is the parent, and ices is failing to reap its child processes when they exit.
As for why, I don't have a clue... it's pretty certain to be a bug of some sort, and it appears to happen exclusively on CentOS 6.3 according to the reports we've received, so clearly something has changed (perhaps in the default kernel used by CentOS 6.3 or somesuch) to bring this bug to light.
FWIW, I've created several CentOS 6.3 VMs and ices has worked fine on all of them, which is somewhat puzzling. We'll continue to investigate as best we can but just a reminder to everyone that ices is NOT our product and we are NOT the developers of ices, so our recourse is somewhat limited here.