Yea but back heat only warms the air. Since the tubs are so small, it really doesn't give them a huge gradient imo. If you kept the room at a constant 85deg i bet that balls would be fine. There'd be a bit of risk involved just bc thats not the norm, but id like to see how it turns out.
I keep my bps a bit cooler than a lot of people and they do fine. My hotspot averages 87 (between 86-88) and the cool side is usually mid 70s. I know a lot of people keep the hot sides at 90 and above though.