Can tubes be used in tubeless rims as well as tires?
Yes - take off the tire and the tubeless valve, clean up the rim, put on some new rim tape and then install a tube + tire. 

If you're running tubeless and you have a failure, you can always just pop a tube in and continue your ride. And tubeless has its advantages (lower pressures since you can avoid pinch flats), so you may want to embrace it.