<p>Can ZK easily be integrated in a struts web application?</p>

maybe you can find it interesting:
http://www.zkoss.org/smalltalks/zk-sample/zk-sample.html
moreover, you can browse a bit the zk forum you can find on
http://www.zkoss.org/
itself, it is more than easy to find some discussion about that.
hope it can help
luca