To answer your question, it is not necessary to mulch; however, good mulching techniques can be very beneficial to bananas and plants in general. In my own garden I make extensive use of mulching with seaweed as it's excellent at moisture retention and keeps the soil cooler, along with adding lots of micro-nutrients and growth hormones to the soil (breaks down fairly quickly too). I have a tamarind tree in the yard that I got to start growing (after it hadn't done anything for years) by mulching with lots of seaweed
