I'm pretty sure your don't need an Arc Fault breaker for hot tubs. It's been a LONG time since I have done anything electrical but this doesn't seem accurate. It does need to be GFCI protected. I'd look into this....

As mentioned, Goldline, Jandy, etc are pool/spa controllers that can control the temp but I'm not sure if they have a way to communicate out if the water temp drops below a certain °. The Goldline PS4's and PS8's we've controlled haven't. Maybe Jandy does. I looked into integrating an Winland EnviroAlert with a temperature probe but we never ended up doing it. The EnviroAlert would give you the ability to do a local alarm and use an alarm panel, some sort of dailer, or anything that can send out push notifications.