That thing (specifically the smaller slots) is going to be near impossible to keep clean, and as you've already pointed out, it won't be available to provide belly heat whatsoever. In addition, since you will be back-heating all the slots the same way, you really won't be able to effectively regulate ambient temps in a consistent manner (the larger slots have many times the air volume of the smaller ones).
I would seriously sit dad down and explain that tubs are not cruel, and regardless of his opinion on the matter, experts with years of experience with these animals have found through trial and error they are the best for the animal and the breeder, and swear by them.