Without a doubt, GMRS and FRS radios could and would be used in an emergency. As has already been stated, many CERT organizations use them. More importantly, they will be most useful to you and your family if you and your family know how to use them, know how you will use them, and you are prepared to use them on zero notice (which means having them with you and having ample power source (aka batteries) available. Knowing how to use them goes beyond powering up and setting channel.
GMRS and FRS provide for good short-distance comms. GMRS may give you greater effective range in an emergency, but only if the local repeaters you are accustomed to use remain in service. The more local repeaters you know about and have programmed into your radio the more longer range options might be available to you. This is also true of amateur radio comms. The distinct advance amateur radio has over GMRS and FRS is the wide variety of equipment types and frequency bands available to them. Many amateurs practice on the radio weekly, and many daily. I fall into that later. Preparing means know what you options are and how to take advantage of them.
Although it is a bit late, there have been a couple of recent YouTube videos published regarding how GMRS is now being deployed and used in places like California in the wake of the Paradise fire. But remember, prepping is always to late after the emergency situation has arrived.
I'm curious to know if GMRS can be used to coordinate disaster response activities? I'm thinking of a hurricane strike zone or something similar. The FCC stipulates licenses assigned to individuals which can also be used for commercial purposes, but only by licensed individuals or their direct family. So I'm confused as to whether or not GMRS could be called into service to coordinate disaster response activities temporarily in various areas that may be stricken.