Deeceer,
You are correct in your findings about there being holes where the arm rests would go, but thats not the end of it....
The VW Captains seats have extra bracketing that criss crosses the back of the seat from where the holes are down to the base.
There is also a brace that goes across between the holes.
These items have to be in place because of the stress that is forced through the seat upright.
This discussion has been talked about on the UK forums lots and lots because the captains seats are very expensive to purchase second hand.
Some people were driving to Germany to collect as many captains seats as possible and selling them in the UK.
There was a part number on the VW computer for the bracing i am talking about but i believe it had to be welded into the seat frame.

Those FASP seat swivels that you linked to are the best made swivels i have seen.
I have seen many different ones made including two sheets of steel with a blot through it in the middle!!!
Cheers Rob