As my wife quickly pointed out after I sent this to a friend with diabetes, this only applies to those with Type 2. In the article it does state the those with Type 1 diabetes should avoid hot tubs as it can lower their blood sugar.
Here's the quote from that article:
Others who might want to avoid the hot tub include those with type 1 diabetes (blood sugar may drop too low) or heart disease, pregnant women, or anyone who gets dizzy easily when standing up (many of the patients felt shaky after their soak).