Is it ok to run a heat pump when the fan on the outside isn't turning.but cool air is blowing through the vents?

It will run until the high pressure safety switch (assuming you have one) trips it out or the compressor dies if you dont have one. If you must run the ac, put a lawn sprinkler or a hose nozzle set at mist and aim it on the coil to keep it cool until the fan can be repaired.