Someone78, thanks that was what I needed. I did have to do one other thing to make it work, found it down further in the changelog.
The following needs to be added before the closing } in resource/modevents.res to use the zombification event in other plugins.
Code:
"zombification"
{
"userid" "short" // user ID who was zombified.
"attacker" "short" // user ID who killed.
"class" "short" // class ID who zombified.
}