ZoneAlarm normally uses the latest Kaspersky engine (SDK) and detects the same threats Kaspersky does. However, it uses only the scan engine and not System Watcher or anything else. Just like Bitdefender and Emsisoft or Avira and F-Secure.
They can’t be using old engines, as this might put users at risk.
I see no reason to go for ZoneAlarm, as Kaspersky is a lot lighter and already one of the leaders.