YES.
Yes, heat does affect fertility- especially for the guys.
On one occasion I ran into one of my customers and asked him how his spa was,... his responce was, "Im not allowed to use it..." When I asked why, we had a short discussion about how the hot water was affecting his 'guys'...
One step further; I saw once- and cant remember where exactly- there were some men (Scandinavian I think.) experimenting with soaking thier testicles in hot water as a means of birth control. These fellas seemed to make a science of it, even creating a chair, not unlike a 'potty' chair so they could sit as they soaked their family jewels in piping hot water. Apparently, they have had good success with it...though like everything else- not a 100% reliable.