Both services are active during emergences with the larger base being amateur radio because of its existing infrastructure and recognition by emergency service agencies from fire, law and Red Cross. GMRS/FRS can't compete due to a single frequency band, lower allowed power and lack of a national organization setting up recognized guidelines. In some areas where evacuations are more common you will find a lot of people using the FRS bubble-pack radios but with no real coordination or information sharing.
One suggestion I'll make is try to dig a little more into the setup on that (or any) repeater before pinning your plans on it, primarily whether they have backup power in case grid power is down.
