Relationship between /scan and /map

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This depends on what settings you use. http://wiki.ros.org/hector_mapping

The description of the map: "Get the map data from this topic, which is latched, and updated periodically " And we having settings such as: "laser_max_dist" and "laser_min_dist".

Does the occupancy grid update 1:1 with our scan? Or does the scan go past our occupancy grid (or vice versa)

No, especially when the scan can likely be 50hz and higher, the map will be updated periodically (this does not mean the algorithm can't process all the scans). In fact, the publish rate of the map is based on the parameter "map_pub_period" which will at default publish the map at 0.5Hz. See here.

If you use laser_max_dist and laser_min_dist with a narrow interval the scan will go far beyond the occupancy grid.