If the batteries you choose have an adequate C rating, and the ESC is rated for the maximum voltage the battery will supply no harm should come to either the ESC regardless of the type of battery used. Voltage is voltage no matter the source (type of battery) so you will have only two concerns; first is the battery capable of the peak current that will be pulled and second on how to NOT over discharge the battery. If using LiFe you will have to carry more mass for equivalent duration and will need to reprogram the cut off point on your ESC.. Bottom line, yes you can use LiFe instead of LiPo as long as you meet the above requirements.