Nice solution - what I do is - 1)add the vlan/description/range in the scan targets like you did... and 2) go to IP Location configuration, take those ranges, and add the five of them with the exact same name. So, BAM - every report that uses IP Location will now have all of those VLANs rolled up in one location. Plus, reporting on dynamic asset groups is a pain in the you-know-what, versus a left join on tsysiplocations table for whatever report you want to make.
Or, do both solutions and see which one you like best!