They are not heated but you can buy small flat heaters that are perfect for bowls, let me see if I can find a picture of them online..
There you go, its called a hydro mini heater, I've used them, they're not very powerful and can't heat 5 gallons like it says they can. They are perfect for 1-2 gallons. They don't have a heat setting so just make sure you get a thermometer so you can make sure they're not eating the water too much. But I've used them in a 1 gallon and the temp was always a comfortable 78-80 degrees
You're diet sounds great. Freeze-dried foods should only be fed as a treat though, not a stable diet as they can cause severe constipation. In my opinion Hikari betta pellets are the best out there, I feed those mixed with Topfin color enhancing betta pellets twice a day and a snack of thawed bloodworms every other day.