Yes, SearchBlox will automatically index custom meta fields within HTML pages, and these custom fields will be returned as part of the search results. You can also perform fielded searches against these fields.
For example, in an HTML page, there is a custom meta field <meta name="section" content="WORLD">. It will be automatically indexed, and you can narrow your search results by doing a search section: WORLD to get all pages that contain this meta information.
If you need the content from meta field or custom fields to be searchable, add the following mapping to the mapping.json file found within the /searchblox/WEB-INF folder, restart Searchblox and then create a new collection to index the pages:
Now you can perform searches on the content of the custom field.
To learn more on custom fields in search read: Custom fields in Search in SearchBlox