Hi,
Any notices regarding diabetics would have been put up as a precautionary/advisory measure, not to ban the D.
Just health and safety for anyone who happens to be diabetic..
Indeed insulin sensitivity can be increased with heat from a sauna or hot water. But this can be dealt with by lowering insulin & monitoring the blood.
Neuropathy may be an issue with regards to feeling higher temperatures & not noticing scalding.. Again, this is just a case of making sure the temp is within safe tolerances..
To be honest I've done Indian & Swedish saunas & never seen any signs..
The methol sauna I had in Kodaikanal was like chemical warfare..!