Yes you can tell by the jaw structure, but the big give-away is the teeth, long and sharp for catching fish. AFAIK all Gymnothorax spp. will have those teeth.
Make certain your tops are tight since chasing the other out of the tank is the preferred method of eel on eel homicide. Other than that, you will see some damage and loose flaps of eel hide if there is a problem, the struggles usually don't begin as 'to the death', but the continual damage will definitely cause death.
good luck, I love the yellow head morays (fimbriated).
bb