Imaging live server

Newer versions of Symantec Ghost have a "hot imaging" feature that allow you to image the startup drive of a Windows machine while it's up and running. I'd like to be able to do something similar with OSX server. First off, can hdiutil image a startup disk that's in use? I'd also like to be able to make incemental updates once the initial disk image is created. I'm curious to hear what strategies others are using to accomplish this type of thing.