We just set up an iPad to do Mobile Sync with our Zimbra farm, and everything seems to work just fine.
What doesn't work fine ("yet", we hope?) is the ZCS Advanced web interface; there are no scroll bars in the mail list window nor in the message preview window. So if you are on OSS, you are limited to the Standard HTML only web interface.
I added to the existing RFE in Bugzilla to ask for the above use case to be coded in to Zimbra. Bug 45905 - ipad support for mobile lite client
Hope that helps,