I'm fairly certain I was able to just 'aptitude install gitit' on debian stable, edit the config file and 'gitit -f gitit.conf' to be up and running.
But you cannot grab some software sources from dev repos (e.g. git clone gitit) and then install the required libs from apt and expect it to work. It may work if all the dependency libraries are very mature and stable, but that's not usually the case.