Yes. An 18650 battery pack can operate without a BMS board, but it’s not recommended.
You can use a balance charger to monitor the current and voltage while charging the 18650 battery pack, but without a BMS for 18650 battery pack, there is no way to monitor the balance of the battery and input while discharging, both of which are important.
MORE: How to determine which BMS can be used in Li-ion bl-5c batteries or Li-ion batteries?