Can a 7.62x39mm round be safely fired from a 30-06 rifle?

No, No, No, 30-06 is 7.62x63, 39 and 63 being mm of case lenght. If the rifle was pointed up and the round had fallen back and was possibly hit by the firing pin the round would not be in the chamber resulting in a bullet flying around in the receiver and possibe"loss of face".