Search and the Django-CMS
Currently the best way to integrate search with the Django-CMS is Haystack, however it is not officially supported.
If you go the Haystack way, you'll need a search_indexes.py. Haystack doesn't care if it's in the same app as the models, so you can put it into any app within your project.
Here is an example untested and unsupported search_indexes.py: