No, cellular ability on the apple watch is not necessary. Our app works with any Apple Watch series 1, 2 , or 3. The LTE (cellular) watch model is not required.
Data is passed between the watch and paired phone using bluetooth and Wi-Fi which all models have.
The watch application, once fully setup up, can actually use all functionality independently from a phone for as long as you'd like, gathering HR, triggering notifications and recording EKGs.
Any data collected will be transferred to your phone the next time your phone is nearby.