Appreciate this is an old post, but still getting picked up via google so might be relevant.  We have a couple of products spun out of needing an iPhone Zenoss client internally for our engineers to quickly acknowledge events out of hours and on the road.

If you want a quick, free, test then download KyK Lite.  It's the free version that pulls new and acknowledged events using the Zenoss API, and is fairly configurable in what you see. Just enter the hostname of your Zenoss instance and your username and password.  There is a paid for version awaiting approval that allows you to acknowledge events and view logs, and more to come depending on user demand too.

KyK Lite is in the App store via - http://itunes.apple.com/us/app/kyk-lite-for-zenoss/id478591263?ls=1&mt=8

HTH

(Full Disclosure - KyK and KyK Lite are our apps so we have a commercial interest - but then we wrote them because we needed them, like the OP!)