Hi Stalwart
Kiln dried is for between all block paving.
I understand that some people do use joint stabilisers and suppliers sell various additives. Not sure they are ideal for flexible paving but can't comment for sure as we've neber used.
Quote below is from the link you posted: -
Dry Sand Jointing
"This method is used on all flexible block pavements, and on pavements constructed using small element pavers. It is also used with some decorative patio flags where a mortar joint is not required.
Three important points to note:
1. there is NO cement used: None, nil, zero, zilch, nada, neamhní, nowt.
2. the sand used is specially selected
3. the surface must be dry
Building sand, playpit sand, beach or river sand, grit, coarse, bedding, soft and plastering sands are not normally suitable. The sand to be used consists of grains that fall within an upper and lower size range, to ensure maximum interlock between grains".