Deep frying with tallow in a stainless steel pot
I don't think you will have the risk of fire, as long as you keep the oil in the pot. Temperature will modulate more quickly than in cast iron, but it is not going to vary much within the pot itself.  I use a wok because the slanted sides make for safer deep-frying. So, you don't need cast iron.   In a pot, you need to be careful that when you add your ingredients, the oil does not boil over.  So, I would recommend filling less than 1/2 way, and using a thermometer to monitor the temperature.