This project is taking some time, BUT i now have more definitive info from support at HikaShop.

Here is their suggestions;

"I know you can't add the products one at a time. That's the goal of the import system to add a whole bunch of products together in one go. So it doesn't change what I said so far.

And you can't pre create the categories via the interface ? Will the categories change in the future ?
If yes, then I do understand that you want to have the CSV embed the hierarchy of the categories in it.
In that case, you can have empty lines at the begining of your CSV with just the categories hierarchy and then just mention the categories in the products."

Here is an example of the Categories and 2 level of sub-Categories using an easier to understand product example set;

"parent_category,categories,product_name
FOOTWEAR,FOOTWEAR_MENS,
FOOTWEAR,FOOTWEAR_WOMENS,
FOOTWEAR_MENS,FOOTWEAR_MENS_DRESS,
FOOTWEAR_MENS,FOOTWEAR_MENS_SPORTS,
,FOOTWEAR_MENS_DRESS,product 1 in the dress category
,FOOTWEAR_WOMENS,product 2 in the womens category"

In practice, the actual Categories have more obscure titles but follow the same concept of Master Category and up to two levels of sub-Category.

In the original Polycom Conference room Equipment Spreadsheet all/only the Categories are in column A and they can only (I think) be differentiated by the cell formatting thus;
Main Categories are all caps.
Child Categories have a leading cap followed by lower case, and have a shaded cell background and Grandchild categories have leading cap followed by lower case and no cell background.
I cannot see any other way to differentiate one category from another.

All together the original spreadsheet has several hundred+ categories and 2,000+ Products.

The original Excel sheet is updated every month, and therefore the updating of the .csv must occur automatically, and can be run through CRON to further automate the upload to HikaShop.