Hi lebrob, and welcome to the forums!
I hadn't heard of the Xaus Lodge until I saw your post, but I had noticed how there were areas marked "Mier Heritage Ground" and "SAN Heritage Ground" on the Map of KTP.
These areas are on the south-west border of the park.
After some googling I found the Xaus Lodge website
and an interesting article about the lodge .(removed non-working link)
From the pictures on the websites, it looks very beautiful.
Peace Parks Foundation website wrote:
Of greater significance however is the spirit of reconciliation encapsulated by the name !Xaus. The lodge and its specific location is the positive outcome of a land settlement agreement reached between the South African Government and South African National Parks with the Khomani San and Mier communities to whom the land originally belonged before its incorporation in 1931 into the then Kalahari Gemsbok National Park.
This landmark agreement has allowed traditional communities to regain their dignity and ownership of the land of their ancestors. Their desire to ensure responsible tourism to this ancestral land has led them to enter into an innovative partnership with South African National Parks, who have retained responsibility for the management of its environmental integrity and with Transfrontier Parks Destinations, who have been appointed as the tourism managers of the lodge and its activities. The Khomani San and Mier, in their traditional spirit of community sharing, are now again able to welcome visitors to their own land and to share with them the magic aura of the Kgalagadi Transfrontier Park.
Judging from the KTP map and from the above, I would assume that it is a sort of concession - but on Heritage Ground not SANParks land. The implication to me is that there are no fences, and that SANParks is responsible for the environmental management of the land.
Hopefully one of the gurus (or someone else who knows) will be able to give more insight.