Not sure what level of integration you require, but you may find the below useful if integration is only to move content periodically from UCM to Sites:
- Write a standalone java code to connect to UCM and export content as xml (use API/RIDC)
- Java code to parse the xml and convert to a format/structure accepted by XMLPost utility of Sites (use XPath parsers for ease)
- Run the XMLPost utility to inject content into Sites
- Schedule the above steps using shell script and crontab
There are a number of approaches to doing this, and it totally depends on the version of UCM you're using (and the version of Sites too for that matter). Have a look at this presentation that Bex Huff and I gave at Collaborate last year.