Gracie certainly can't tolerate it..when we are outside out in the pool and she comes out I make sure she has plenty of fresh water and we leave the sunroom door open so she can go in and out and there is a fan in there and sometimes she STILL throws up..from either drinking too much water too fast or getting too hot running after a squirrel ..so if it is over 95 I just don't let her stay out long...unless she gets in the pool with us to cool off some.
Maybe it is what they get used to...she is used to being in AC most of the time except to go potty or if we go out in the evenings to sit when its not so hot so she can play.