Because he does not use a hot spot does not mean he should not have one unless you are of course keeping the ambient temp in the mid 80's
They need a hot spot or higher ambient temperatures that what is called having PROPER husbandry, and whether you use a UTH with a tanks a pvc cage all you need is a thermostat.
Proper temps are important not only for digestion but also overall health, improper temps lead to stress, stress with improper husbandry lead to heal issues such a RI