From the documentation:
BasePress was developed with a search feature of its own which filters the results according to the Knowledge Base visited, by language when used with WPML and by BasePress content restrictions. This add-on makes it possible to use SearchWP retaining the automatic filtering of the content. Also the add-on is necessary for SearchWP to power BasePress live Ajax results as well.
BasePress Knowledge Base + SearchWP Integration is a 3rd-party plugin. Please contact the BasePress support team for more information or other questions.